Catalogue of Organisms

Thistle Be The One (Taxon of the Week: Carduoideae)

noreply@blogger.com (Christopher Taylor) — Mon, 09 Nov 2009 03:54:00 +0000

The cardoon Cynara cardunculus with humans to scale. Photo from here.

The composite-flowering plants of the Asteraceae are one of the largest (23,000 species, according to Wikipedia) and most distinctive plant groups out there - even a complete botanical dunce like yours truly can usually recognise an example of Asteraceae. Asteraceae include such plants as daisies and chrysanthemums in which the "flower" is in fact a large number of tiny flowers all pressed together, hence the old name for the family of "Compositae". Different authors have proposed different classifications within Asteraceae over the years, but twelve subfamilies were recognised by Panero & Funk (2008). The subfamily Carduoideae as recognised by these authors includes the three tribes Dicomeae, Tarchonantheae and Cardueae (earlier authors had used the name to cover a broader paraphyletic assemblage, or restricted it to include only Cardueae). The genus Oldenburgia may be included in Tarchonantheae or it may be placed in its own separate tribe (Funk et al., 2009). No unique morphological features characterise this subfamily (though most species have a ring of papillae on the style underneath the stigmatic branches), but it is well supported molecularly.

The tribes Dicomeae and Tarchonantheae are primarily found in Africa and Madagascar (two species of Dicomeae and one of Tarchonantheae are found in Asia). The seventeen species of Tarchonantheae (including Oldenburgia) are all shrubs or trees; the 75-100 species of Dicomeae include herbs, shrubs and trees. Tarchonantheae includes the genus Brachylaena, species of which predominate in southern African and Madagascan woodlands. Brachylaena species are noted for producing dense, high quality wood, and are also among the largest of the Asteraceae, reaching 40 m in height (Beentje, 2000).

Brachylaena discolor from southeastern Africa. Photo from here.

The largest by far of the three tribes is the Cardueae*, the thistles, with some 2500 species distributed through Eurasia from the Mediterranean to central Asia. The majority of Cardueae are herbs, though there are a few small shrubs or even small trees in the tribe. Most members of Cardueae have distinctive discoid flower heads** and, of course, many have spiny leaves.

*I have just been through the painful, arduous and not-entirely-productive process of trying to decide whether 'Cardueae' or 'Cynareae' is the correct name for this tribe; both names are used regularly. Lamarck & de Candolle published the name 'Cynarocephalae' in 1806 (Reveal, 1997); Cardueae was published by Cassini in 1819 (Solbrig, 1963). The question therefore hinges on whether the '-cephalae' in Cynarocephalae represents a suffix like '-idae' or '-aceae' or whether the name is descriptive of plants with 'heads like Cynara'; if the former, Cynareae has priority from 1806; if the latter, Cynareae was not published until 1830 (and illegitimately so at that) and Cardueae has priority. Botanists still seem to be in the process of duking out which interpretation is corrent, and I suspect that it may take the ICBN stepping in to settle the matter.

**Composite flower heads may contain both 'ray' and 'disk' florets (the little individual flowers). If you think of a daisy, the 'ray' florets are the ones around the edge that carry the large petals while the 'disk' florets are the central ones without petals. Discoid flower heads like those of Cardueae contain only disk florets and no ray florets.

Side view of flower head of Atractylis cancellata, a Mediterranean thistle species in which the rosette of (particularly evil-looking) leaves around the flower head curls upwards to surround it. Photo by Manuel Ramos.

Species of Cardueae most often bring themselves to humanity's attention through the fact that a number of them are significant weed species, and very few Cardueae are regarded with any sort of affection. The Scotch thistle Onopordum acanthium is of course popular in Scotland where it is the national flower; according to legend, a Scottish encampment was saved from a sneak attack by Vikings when one of the invaders yelled out after stepping on a thistle, alerting the sentries to their presence. Also granted a certain regard is Cynara cardunculus, the cardoon/globe artichoke. Earlier classifications recognised two species, the cardoon C. cardunculus grown for its edible stalks and the artichoke C. scolymus grown for its similarly edible flower heads, but there is no doubt that the latter is a horticulturally derived variety of the former. Perhaps the best demonstration of this is that escaped seeds from artichoke fields in California and Australia have given rise to wild populations of 'cardoons' (Sonnante et al., 2007). I will also note that artichokes would also be a feature of my ideal garden - not because I'm a fan of eating artichokes (I think they're pretty tasteless) but because these two-metre tall thistles are such spectacular plants.

And that's all you'll be hearing from me for a little while - five-thirty tomorrow morning, I leave for two weeks in the field. Feel free to talk among yourselves until I get back.

REFERENCES

Beentje, H. J. 2000. The genus Brachylaena (Compositae: Mutisieae). Kew Bulletin 55 (1): 1-41.

Funk, V. A., A. Susanna, T. F. Steussy, & H. E. Robinson. 2009. Classification of Compositae. In Systematics, Evolution, and Biogeography of Compositae (V. A. Funk, A. Susanna, T. F. Stuessy & R. J. Bayer, eds) pp. 171-189. International Association for Plant Taxonomy (IAPT): Vienna.

Panero, J. L., & V. A. Funk. 2008. The value of sampling anomalous taxa in phylogenetic studies: major clades of the Asteraceae revealed. Molecular Phylogenetics and Evolution 47 (2): 757-782.

Reveal, J. L. 1997. Early suprageneric names in Asteraceae. Compositae Newsletter 30: 29-45.

Solbrig, O. T. 1963. Subfamilial nomenclature of Compositae. Taxon 12 (6): 229-235.

Sonnante, G., A. V. Carluccio, R. Vilatersana & D. Pignone. 2007. On the origin of artichoke and cardoon from the Cynara gene pool as revealed by rDNA sequence variation. Genetic Resources and Crop Evolution 54 (3): 483-495.

"Electronic Publication of Nomenclatural Acts is Inevitable"

noreply@blogger.com (Christopher Taylor) — Fri, 06 Nov 2009 07:21:00 +0000

The Jurassic mecopteran Lichnomesopsyche gloriae, one of six new fossil species not published today. The black line is highlighting the long proboscis; the scale bar represents 10 mm. Image from Ren et al. (2009).

So sayeth Mike Taylor (for my own confused ramblings through the quagmire of electronic publication, read my earlier posts on the subject). And this day presents us with a spectacular demonstration of that point.

In a paper in today's issue of Science, Ren et al. (2009) have presented an analysis of Jurassic to early Cretaceous long-proboscid scorpionflies and their role as probable pollinators of nectar-producing gymnosperms (as has also been suggested for kalligrammatid lacewings). As part of this study, Ren et al. present descriptions of six new species and two new genera of fossil scorpionflies. Nothing out of the ordinary here, except that (Science being Science, with its notorious restrictions on article length) the species descriptions are published in the Supporting Online Material.

From the point of view of the ICZN, Science is a perfectly valid forum for publication - thousands of copies are printed every week. But these printed editions don't include the online supplements, so the online-only component of the journal is currently not a valid publication. Technically speaking, the new species of Ren et al. (which are referred to and illustrated but not described in the print version) are nomina nuda. They are not valid names. But these online-only names have not appeared in some far-flung unfrequented corner of the internet, they have appeared in one of the world's most prominent science journals (like it says on the label). Their validity is going to be pretty much taken for granted.

REFERENCES

Ren, D., C. C. Labandeira, J. A. Santiago-Blay, A. Rasnitsyn, C.-K. Shih, A. Bashkuev, M. A. V. Logan, C. L. Hotton & D. Dilcher. 2009. A probable pollination mode before angiosperms: Eurasian, long-proboscid scorpionflies. Science 326: 840-847.

Name That Bug: Ponopterix axelrodi

noreply@blogger.com (Christopher Taylor) — Fri, 06 Nov 2009 03:49:00 +0000

Ponopterix axelrodi (from Bechly, 2007).

Obviously I'm going to have to refrain from using fossil insects as ID challenges in future, or at least confiscate Adam Yates' copy of Grimaldi & Engel (2005) before I do so to stop him from identifying them so quickly*.

*Unless, of course, I cruelly exploit Grimaldi & Engel's neglect of Palaeozoic polyneopterans.

Ponopterix axelrodi is a member of the Jurassic to Cretaceous insect family Umenocoleidae from the Lower Cretaceous Crato Formation of Brazil. Umenocoleids were originally described in 1973 as beetles, which they resemble in having the front pair of wings hardened into a pair of elytra (wing covers). However, while elytra are only found in two orders among the Recent insect fauna (beetles and earwigs), umenocoleids represent a third independent origin of elytra and are in fact related to dictyopterans (the clade that includes cockroaches, mantids and termites). The retention of a short ovipositor in Umenocoleidae (visible in the specimen above at the very end of the abdomen) places them just outside crown Dictyoptera, though a position closer to polyphagoid cockroaches has also been suggested (which would imply more than one loss of the ovipositor among dictyopterans).

As Adam pointed out, umenocoleids differ from beetles in that wing venation is still marginally visible on the elytra (among crown-group beetles, the original venation has been completely obliterated) and in the presence of cerci (two tail-like appendages at the end of the abdomen, one on either side of the ovipositor in females; cerci are absent in paraneopteran and holometabolous insects). The anterior light patch at the base of the elytron in the specimen above is also present in another specimen of the same species illustrated in Grimaldi & Engel (2005), so this was the original colour pattern of the animal when it was alive*.

*Don't let the poor reputation of cockroaches put you off - many roaches are very attractive insects, boldly patterned in contrasting colours**.

**Just be careful of the desert cockroaches that walk around with their backsides pointed into the air. If they feel that a potential threat is approaching too close, they can fire a stream of foul-smelling liquid towards it from a pair of abdominal glands. Not pleasant.

Umenocoleids also inspire the one detail in Grimaldi & Engel (2005) that causes me to scream with frustration. In the caption to their photo of Ponopterix axelrodi, G & E make the remark, "Umenocoleid roaches are known from the Late Jurassic to Cretaceous, though a putative living species exist". A living umenocoleid? Tell me more! Unfortunately, Grimaldi and Engel provide no citation for this statement, and I have been unable to find any reference to a living umenocoleid anywhere else. I'm still holding out hope, though.

REFERENCES

Bechly, G. 2007. 'Blattaria': cockroaches and roachoids. In The Crato Fossil Beds of Brazil: window into an ancient world (D. M. Martill, G. Bechly & R. F. Loveridge, eds). Cambridge University Press.

Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press. 755 pp.

Name That Bug # 4

noreply@blogger.com (Christopher Taylor) — Thu, 05 Nov 2009 04:54:00 +0000

Another fossil for you all. Scale bar is five millimetres; attribution, as always, to follow.

Update: Identity now available here. Photo from Bechly (2007).

Name That Bug: Meioneurites spectabilis

noreply@blogger.com (Christopher Taylor) — Tue, 03 Nov 2009 07:55:00 +0000

Meioneurites (Parameioneurites) spectabilis (from Engel, 2005).

This image wasn't up ten minutes before being identified by Adam Yates. Meioneurites spectabilis is a member of the Jurassic butterfly-like lacewing family Kalligrammatidae. Kalligrammatids have been featured on Catalogue of Organisms previously.

In the fossil above, you can see that kalligrammatids lacked the coiled proboscis of a butterfly (though their mouthparts are much more elongate than other lacewings, and kalligrammatids were probably nectar feeders like butterflies). Also, if you look very closely at the wings (you'd probably have to zoom in), you may be able to make out that there is a higher density of veins in the wings than in butterflies.

For comparison, here's another kalligrammatid, Sophogramma lii, in a figure from Yang et al. (2009). Pretty.

REFERENCES

Engel, M. S. 2005. A remarkable kalligrammatid lacewing from the Upper Jurassic of Kazakhstan (Neuroptera: Kalligrammatidae). Transactions of the Kansas Academy of Science 108 (1-2): 59-62.

Yang Q., Zhao Y.-Y. & Ren D. 2009. An exceptionally well-preserved fossil kalligrammatid from the Jehol Biota. Chinese Science Bulletin 54 (10): 1732-1737.

Name That Bug # 3

noreply@blogger.com (Christopher Taylor) — Tue, 03 Nov 2009 04:53:00 +0000

Mr Greenslade, tell the masses what's the challenge:

Perhaps a little easy, but I'm feeling charitable. Size of image about ten centimetres across. Attribution, of course, to follow identification.

Update: The identification post for this image (from Engel, 2005) is now available here.

Cranes Off the Rails (Taxon of the Week: Grues)

noreply@blogger.com (Christopher Taylor) — Mon, 02 Nov 2009 02:53:00 +0000

The 'Messel rail' Messelornis cristata - a specimen with preserved plumage. Photo from here.

Despite its presentation in years of fieldguides and other popular books, the bird order 'Gruiformes' has in recent times been scattered to the four winds, with analyses both morphological and molecular proclaiming its polyphyly. Nevertheless, molecular analyses such as Hackett et al. (2008) continue to support a clade roughly corresponding to the suborder Grues as recognised by Cracraft (1973)* containing the cranes and the rails. The morphological analysis of Livezey & Zusi (2007) on the other hand, does not support this clade, but it does support monophyly for each of the two primary divisions within Grues, the ralloid and gruoid lineages.

*Just to confuse matters, the name "Grues" has been used by different authors for clades of differing inclusivity. Mayr (2009), for instance, uses "Grues" for the Aramus + Gruidae clade, and refers to the larger clade as "core Gruiformes".

The ralloid line contains the living families Rallidae*, the rails, and Heliornithidae, the finfoots (or should that be finfeet?) Cracraft (1973) regarded the Cretaceous Laornis edvardsianus as a stem ralloid, but no-one else seems to have taken him up on this suggestion. More reliably on the ralloid stem are the Palaeocene to Oligocene Messelornithidae (Mayr, 2009). Messelornithids were medium-sized birds (about the size of a small chicken) best known from Messelornis cristata for which over 500 specimens are available, some even with preserved feathering. Messelornis was highly terrestrialised with limited flight capabilities and almost ludicrously long legs (loss or reduction of flight has been a common occurrence among the Grues). Its beak was relatively short and the overall appearance of Messelornis would probably have not been dissimilar to the modern cariamas.

*Hackett et al. (2008) resolved the Rallidae as paraphyletic to Heliornithidae, with Sarothrura (the flufftails) closer to Heliornis than to the other two included rails Himantornis and Rallus. A few places, at least online, have suggested recognising Sarothrura as a separate family from the Rallidae as a result, but I'd recommend waiting for a more detailed analysis with greater coverage of the Rallidae. Increased taxonomic coverage may return the flufftails to the other Rallidae, or it may make it more appropriate to treat the finfoots as derived rallids.

The sungrebe Heliornis fulica of tropical South America (I tried to find a picture of one carrying chicks, but no luck). Photo by Jerry Oldenettel.

The finfoots of the Heliornithidae are three species (one in Asia, one in Africa, one in South America) of tropical grebe-like birds, renowned for their reclusiveness. The South American sungrebe Heliornis fulica is the most distinctive in appearance of the three species (though mitochondrial analysis indicates that it and the Asian Heliopais personata form a clade to the exclusion of the African Podica senegalensis - Fain et al., 2007) and is also very distinct in its nesting behaviour. Heliopais and Podica, like most aquatic birds, have chicks that hatch out reasonably well-developed and immediately able to swim after their parents. Heliornis, in contrast, has altricial chicks that hatch out after only ten to eleven days of incubation. The really amazing bit, though, is what happens after the chicks hatch. The male sungrebe has a shallow pouch under each wing and he is able to transport the chicks inside this pouch, even flying with them. Whether the chicks remain in the pouches permanently or whether they are only placed in them while the male is travelling remains unknown. Funnily enough, while this chick-carrying behaviour was described by Alvarez del Toro in 1971, it had originally been recorded almost 140 years earlier by Prince Maximilian of Wied. It seems that everyone else had assumed the prince was smoking something.

Grey-winged trumpeters, Psophia crepitans. Photo by A. Vinot.

The gruoid lineage includes Psophia, the trumpeters, Aramus guarauna, the limpkin, and Gruidae, the cranes, as well as the fossil taxa Parvigrus pohli, Geranoididae and Eogruidae. Most recent authors agree that Aramus and Gruidae form a clade to the exclusion of Psophia. The chicken-sized Oligocene Parvigrus was originally described by Mayr (2005) as sister to Aramus + Gruidae, but he later (Mayr, 2009) revised its position to stem gruoid. Parvigrus lacked the long beak of limpkins and cranes, as do the Recent trumpeters, three species of similarly chicken-sized birds found in northern South America.

Whether Geranoididae and Eogruidae possessed crane-like long beaks is an unknown factor as skull material for both has not been found. Cracraft (1973) placed both outside the crown gruoids, but Clarke et al. (2005) placed Eogruidae inside the gruoid crown as sister to Aramus + Gruidae. The Eocene Geranoididae have been described only from leg bones (Wetmore, 1933, assigned some wing bones to Geranoides jepseni in his original description of this species but did not describe them) so little can be said about them except that they were large and long-legged. Wetmore (1933) commented on the unusually wide spacing of the trochleae (the 'knuckles') at the end of the tarsometatarsus suggesting that Geranoides had very widely splayed toes, but Cracraft (1969) later attributed to wide spacing to post-mortem distortion. Cracraft (1969, 1973) included a number of Eocene birds in the Geranoididae but admitted a lack of derived characters uniting them; Geranoididae may represent a paraphyletic assemblage of basal gruoids.

Distal ends of tarsometatarsi of the eogruids Proergilornis and Ergilornis, showing reduction of the inner trochlea in Proergilornis and its loss in Ergilornis. Figure from Cracraft (1973).

The Eocene to Pliocene Eogruidae were also decent-sized long-legged birds from central Asia and (in later times) Europe. Earlier authors recognised two families, Eogruidae and Ergilornithidae, but 'ergilornithids' are now recognised as derived eogruids. Eogruids were highly cursorial birds and a humerus attributed to Ergilornis suggests that it was flightless, though the earlier Eogrus aeola shows no sign of being so (Clarke et al., 2005). Originally three-toed, eogruids showed a reduction in the size of the inner toe, and Ergilornis and Amphipelargus (the latest of the eogruids) lost it entirely (it is easy to present a progression from flying and three-toed to flightless and two-toed, but be warned that three-toed species survived into the Miocene, well after the appearance of the two-toed forms). The only other birds to reduce the number of toes to two are the ostriches, and a relationship between ostriches and eogruids has been suggested in the past (generally in association with the idea that the ratites do not form a monophyletic group). However, Cracraft (1973) confirmed that eogruids were more similar in their fine morphology to gruoids than ostriches, and modern phylogenetic analyses do not support a close relationship of ostriches and gruoids.

Many people carry the impression that flightlessness in birds is associated with lack of predators. However, eogruids evolved flightlessness in an environment in which predators were no rarity (amongst others, they shared their world with such horrors as hyaenodonts and entelodonts*). Similarly, while the exact circumstances in which they became flightless is unknown, modern ostriches (Africa), emus (Australia) and rheas (South America) all live alongside significant predators or at least did so until recently. Obviously, something other than lack of predators is at play here.

*I always imagine Roald Dahl's hornswogglers to be something like an entelodont.

REFERENCES

Clarke, J. A., M. Norell & D. Dashzeveg. 2005. New avian remains from the Eocene of Mongolia and the phylogenetic position of the Eogruidae (Aves, Gruoidea). American Museum Novitates 3494: 1-17.

Cracraft, J. 1969. Systematics and evolution of the Gruiformes (class, Aves). 1, The Eocene family Geranoididae and the early history of the Gruiformes. American Museum Novitates 2388: 1-41.

Cracraft, J. 1973. Systematics and evolution of the Gruiformes (class Aves). 3, Phylogeny of the suborder Grues. Bulletin of the American Museum of Natural History 151: 1-127.

Fain, M. G., C. Krajewski & P. Houde. 2007. Phylogeny of "core Gruiformes" (Aves: Grues) and resolution of the limpkin–sungrebe problem. Molecular Phylogenetics and Evolution 43: 515-529.

Hackett, S. J., R. T. Kimball, S. Reddy, R. C. K. Bowie, E. L. Braun, M. J. Braun, J. L. Chojnowski, W. A. Cox, K.-L. Han, J. Harshman, C. J. Huddleston, B. D. Marks, K. J. Miglia, W. S. Moore, F. H. Sheldon, D. W. Steadman, C. C. Witt & T. Yuri. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 320: 1763-1768.

Livezey, B. C., & R. L. Zusi. 2007. Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. Zoological Journal of the Linnean Society 149 (1): 1-95.

Mayr, G. 2005. A chicken-sized crane precursor from the early Oligocene of France. Naturwissenschaften 92: 389-393.

Mayr, G. 2009. Palaeogene Fossil Birds. Springer.

Wetmore, A. 1933. Fossil bird remains from the Eocene of Wyoming. Condor 35: 115-118.

Name That Bug: Stoecharthrum giardi

noreply@blogger.com (Christopher Taylor) — Sat, 31 Oct 2009 06:44:00 +0000

From Kozloff (1992).

Meet my favourite orthonectid (because we've all got one, right?) Orthonectida are twenty-odd species of uncommon parasites of marine invertebrates. The host of Stoecharthrum giardi is the annelid worm Scoloplos armiger; most orthonectid species are only recorded from one host, but closely related species can be found in hosts of quite different phyla (other Stoecharthrum species, for instance, are found in bivalves and ascidians). As you can see from the scale bar in the drawing of a sexually mature individual above, they are extremely small- Stoecharthrum giardi, for instance, grows up to 0.8 mm in length and less than 0.02 mm in width. To match this small size, mature orthonectids have a very simple anatomical organisation; an outer layer only one cell deep contains an inner mass of developing gametes, with only a very thin layer of a small number of muscle cells between the two (Slyusarev, 2003b). Sexually reproducing individuals leave their host upon maturity to release their gametes in open water. The resulting larvae re-enter a host and produce multinucleate plasmodia within which new individuals develop from germinative cells. However, there appears to still be some disagreement whether the plasmodium represents the parasite itself (Sliusarev, 2003a) or a pathological product of dissolved host cells (Kozloff, 1997). The relationships of orthonectids with other animals are pretty much unknown - they are often classified in the Mesozoa along with the Rhombozoa, another group of marine invertebrate parasites that also have a simple two-cell-layer organisation, but the detailed nature of the cell layers is decidedly different between the two groups and their simple organisations are just as likely (if not more likely) to be the results of convergence as relationship. Similarly, authors have disagreed whether the simple organisation of 'mesozoans' indicates that they are relatively basal within animals or whether it represents a secondary simplification as a result of their parasitic lifestyle. A molecular phylogenetic analysis by Hanelt et al. (1996) placed orthonectids as sister to all other Bilateria while rhombozoans were placed separately within Bilateria, but their topology shows every sign of long-branch attraction when considered in light of subsequent advances in bilaterian phylogeny.

The orthonectid family Rhopaluridae contains four genera, Rhopalura, Intoshia, Ciliocincta and Stoecharthrum*. The genera are primarily distinguished by the arrangement and morphology of the external cells. The first twenty or so rings of cells from the front of the animal (exact number depending on species) more or less alternate between bands of ciliated and non-ciliated cells (the cilia are the animal's main motile organs after it leaves the host). After that, all cell bands are ciliated, but Stoecharthrum and female Ciliocincta are the only rhopalurids really long enough to have a significant extension of the fully ciliated region. With more than sixty cell rings, Stoecharthrum is more than twice as elongate as most other orthonectids; the average number seems to be about thirty rings (oh, and in case you were wondering, the little arrangement of small cells on ring fifteen is the location of the genital pore). Stoecharthrum and female Ciliocincta also differ from other rhopalurids in having the majority of ciliated and non-ciliated cells about the same length; in Rhopalura and Intoshia, the non-ciliated bands are noticeably narrower than the ciliated bands. The primary difference between Stoecharthrum and Ciliocincta, other than Stoecharthrum's greater length, is that Stoecharthrum is the only orthonectid genus in which individuals are hermaphroditic rather than having separate male and female sexes.

*The only non-rhopalurid genus assigned to Orthonectida is Pelmatosphaera, for which I haven't seen a figure. Kozloff (1992) doubted whether Pelmatosphaera was truly related to Rhopaluridae but didn't suggest any alternative placement.

REFERENCES

Hanelt, B., D. van Schyndel, C. M. Adema, L. A. Lewis & E. S. Loker. 1996. The phylogenetic position of Rhopalura ophiocomae (Orthonectida) based n 18S ribosomal DNA sequence analysis. Molecular Biology and Evolution 13: 1187-1191.

Kozloff, E. N. 1992. The genera of the phylum Orthonectida. Cahiers de Biologie Marine 33: 377-406.

Kozloff, E. N. 1997. Studies on the so-called plasmodium of Ciliocincta sabellariae (Phylum Orthonectida), with notes on an associated microsporan parasite. Cahiers de Biologie Marine 38 (3): 151-159.

Sliusarev, G. S. 2003a. [Orthonectida's life cycle]. Parazitologiia 37 (5): 418-427.

Slyusarev, G. S. 2003b. The fine structure of the muscle system in the female of the orthonectid Intoshia variabilis (Orthonectida). Acta Zoologica 84: 107-111.

Name That Bug # 2

noreply@blogger.com (Christopher Taylor) — Fri, 30 Oct 2009 03:53:00 +0000

The first installment of "Name That Bug" seems to have passed rather smoothly, so I think it's time for another. Bit harder this time (maybe), but because I'm a nice guy I'll give you part of the original figure caption as a clue of sorts.

Composite drawings based on silver nitrate and protargol impregnation.

Update: Solution now available here. Image from Kozloff (1992).

Name That Bug: Cornu aspersum

noreply@blogger.com (Christopher Taylor) — Thu, 29 Oct 2009 02:22:00 +0000

Cornu aspersum, aka Helix aspersa, aka Cantareus aspersus, aka Cryptomphalus aspersus.

Phew. The specimen illustrated is a "scalariform" variant of the common garden snail, showing a developmental abnormality where the whorls of the shell, instead of coiling right up against each other, have grown spaced apart. (First ID was by Blackbird, as well as resident malacologists Bronwen and Aydin.) In case by some incredible turn of events you don't have five thousand of them crawling around in your back garden, a normal garden snail looks like this:

The special significance of that particular scalariform specimen is that it is the type specimen of Cornu copiae, type 'species' of the genus Cornu (the image is the illustration that appeared with the original description by Ignaz von Born in 1778). If the garden snail is regarded as distinct enough from Helix pomatia, the edible snail*, to be placed in a separate genus, Cornu is the oldest genus name that has been applied to a specimen of Cornu aspersum. However, there has been a lengthy debate about whether the name Cornu is properly available, which is why some authors have used the genus names Cantareus and Cryptomphalus (the following is based on info from websites here and here).

*So called because its the species most often used for eating. Cornu aspersum is apparently also quite edible, though I've never tried myself. If you do want to eat garden snails, I'm told that you should collect them live and feed them on flour for a couple of days before eating, so that any distasteful plant matter they may have eaten themselves has time to clear from their gut.

The ICZN states that names based on "teratological specimens as such" are not treated as valid names for species (Article 1.3.2). Some authors have therefore claimed that Cornu, whose type specimen is undoubtedly teratological, is invalid. Other authors, whom I would agree with, point out the use of the words "as such" and interpret the rule to mean that names based on teratological specimens are only invalid if they were published with the knowledge that the specimen was teratological (supporting this is Article 17.3 which states that the availability of a name is not affected by its being based on "a specimen which is an unusual example of the taxon"; also, normal vs. teratological is often a matter of degree rather than clear division). The use of Latin names as labels for unusual variants of known species was common practice in the eighteenth and nineteenth centuries (and even a little bit into the twentieth; botanists still follow this practice under certain circumstances). One example of such a label that remains in use today is the reference to the black form of the peppered moth Biston betularia as the "carbonaria form". Such variant names were never intended by their original users to refer to any sort of evolutionarily or populationally distinct "species-level" taxon, which is why the ICZN excludes them. In his original description of Cornu copiae, Born gave no indication that he recognised the specimen as an unusual variant of Helix aspersa rather than a validly distinct species, so we can only assume that he genuinely believed it to be the latter (if he had specifically written something like "this unusual specimen of Helix aspersa to which I give the name Cornu copiae" it would have indicated otherwise).

Oh, and for anyone who might have been wondering why I decided to call this image ID challenge "name that bug" when the animal involved is quite evidently not a bug - i have long come to the decision that "bug" is one of the most meaningless words in the English language. Textbooks tell us that the name is supposed to only apply to insects of the clade Heteroptera (or Hemiptera, depending on the textbook), but I don't know anyone, not even among entomologists, who only ever uses the word "correctly".

Name That Bug #1

noreply@blogger.com (Christopher Taylor) — Wed, 28 Oct 2009 03:21:00 +0000

One downside to no longer being a student is that I no longer have quite so much time to spend on blog posts (well, not if I want to be able to justify my salary), so I'm putting up an image ID challenge instead, and I'll see if I can make this a regular feature. Besides, I've noticed that these tend to be popular at other people's sites, and the reader count in my right sidebar has been edging tantalisingly close to 100 for the last few months. I want to see if I can finally hit the triple digits (the fact that I've never been able to work out exactly what that number represents is irrelevant).

If this works well, I'll try and make it a regular thing. But first up, let's start with a relatively simple one (indeed, if Aydin's reading this, I may ask him to hold off for a bit because he'll probably recognise it instantly):

Tell me what it is, and tell me something about the significance of this specimen.

UPDATE: The identity of this image is given here. The image comes from here.

Time For Teeth (Taxon of the Week: Polygnathus)

noreply@blogger.com (Christopher Taylor) — Mon, 26 Oct 2009 05:20:00 +0000

Lindström's (1974) hypothetical reconstruction of the then-unknown conodont animal as a barrel-shaped floater, with radially arranged conodont elements providing protection from predators dorsally and support for feeding tentacles ventrally.

Conodonts are among the iconic fossils of the Palaeozoic. Minute (in the millimetre size range) but extremely abundant, conodont elements* are tooth-like in appearance. The earliest forms were simple and fang-like; later forms were often blade-like with a median row of teeth. Their abundance and variety mean that conodonts are widely used in biostratigraphy, but for many years the identity of the animal they came from was unknown - whatever it was, it appeared to possess no other hard parts that would normally be preserved. It wasn't until the 1980s that the first unequivocal conodonts with preserved soft parts were discovered, revealing them to be stem- or basal vertebrates** (Sweet & Donoghue, 2001). Each of the conodont animals had a number of conodont elements arranged around the mouth and pharynx. Slender-pointed elements towards the front of the mouth would have seized or filtered prey, while many conodonts also possessed more robust elements further back in the pharynx to grind up their food. The figure below from Dzik (1991) gives a good idea of how it would have all worked, even if the result does look a bit like a carnivorous sock puppet (Dzik's arrangement of the elements has also since been superceeded - see Purnell & Donoghue, 1997, for details). Those full-body fossils of conodonts that have been identified to date are eel- or lamprey-like, but it is worth keeping in mind that only two species of this very speciose lineage are known from such remains and we may not be seeing a proper representation of conodont diversity.

*Before the nature of conodonts was understood, most authors restricted the name to the fossils themselves; the then-hypothetical animal that produced these structures was referred to as a "conodontophore". Since the current identification of conodonts has been accepted, this distinction has been abandoned.

**Conodonts had been found in association with soft body parts before, but the animals concerned are now agreed to have been predators or scavengers of conodonts (with conodont elements in their gut as a result) rather than the conodont animals themselves.

Conodont head in retroventral view as reconstructed by Dzik (1991), with mouth open to show the grasping elements in front and back of head removed to show the grinding elements in back.

Polygnathus has been recognised as one of the largest of conodont genera - some 545 Early Devonian to Early Carboniferous species and subspecies have been assigned to it over the years (Weddige, 2005). Polygnathus belonged to the conodont order Ozarkodinida, and would have had an apparatus of toothed elements similar to that shown below (not Polygnathus, but another ozarkodinidan genus). The lower saw-like S elements at the front of the mouth would have been the initial graspers; the act of opening the mouth would have rotated the curved upper M elements forward, and their rotating back as the mouth closed would have probably drawn the prey in; and the two pairs of large P elements in the back would have sliced and diced the prey.

Reconstructed model of the apparatus of the ozarkodinid Idiognathodus in lateral view, from Purnell & Donoghue (1997).

The Early Devonian members of Polygnathus were recently revised by Bardashev et al. (2002) in what I can only describe as one of the most taxonomically incredible papers it has ever been my misfortune to read. In the early days of conodont taxonomy, working purely from dissociated elements, different elements were treated as taxonomically separate entities. As the recognition developed that a single individual conodont animal would have possessed a number of differently formed elements (something that happened even before the discovery of conodont soft-body fossils as researchers noted that certain element types were always found in association, while specimens were occasionally found in which normally separate elements had become fused together), the older independent element taxonomy was replaced by a multi-element taxonomy based on the apparatus as a whole*. Bardashev et al. (2002), however, base their classification solely on the Pa or P₁ element, the large posteriormost element in the model above. All other elements, they seem to claim, are useless for distinguishing taxa (which could be a problem for dealing with basal conodonts that don't have P elements).

*At least ideally. In practice, of course, there are still a large number of cases in which the correct element associations cannot yet be reliably identified.

On the basis of Pa morphology, Bardashev et al. divide species of Polygnathus between six genera in two families - and this is where things really start to go down the rabbit hole. Members of the family Polygnathidae are divided between the temporally successive families Eognathodidae, Eopolygnathidae and Polygnathidae. Eopolygnathidae are derived from Eognathodidae and Polygnathidae from Eopolygnathidae. Now, the use of paraphyletic taxa is nothing unusual in micropalaeontology. But explicitly polyphyletic taxa? In the phylogeny presented by Bardashev et al., Eognathodidae gave rise to Eopolygnathidae on two separate occasions, with Eoctenopolygnathus descended from a separate group of eognathodids from Eocostapolygnathus and Eolinguipolygnathus (note also that there is no genus 'Eopolygnathus', so 'Eopolygnathidae' is an invalid name under the ICZN). After that, Polygnathidae derives from 'Eopolygnathidae' eleven times - two separate origins of Ctenopolygnathus within Eoctenopolygnathus, four origins of Costapolygnathus from Eocostapolygnathus, five of Linguipolygnathus from Eolinguipolygnathus (the authors refer to these multiple origins as representing common 'trends' between the lineages). Bardashev et al. also name the type species of the new genus Costapolygnathus as Polygnathus dubius, which happens to be the type species of Polygnathus (a point that Bardashev et al. had commented upon themselves earlier in the paper). There are also cases where the type specimens of 'undiagnostic' species are assigned to new species named by Bardashev et al. - surely, if you can identify them to a species, they can't be undiagnostic?

Posterior and anterior views of the Pa element of Polygnathus costatus partitus. Photo from Palaeos.com.

Bardashev et al.'s (2002) reclassification was criticised and rejected by Mawson & Talent (2003), who maintained that because it only covered Early Devonian taxa, it created a strong disconnect in apparent diversity between Early and Late Devonian. This criticism, I must say, is unfair - all revisions have to start somewhere, and to demand an 'all or nothing at all' approach in such cases would be to effectively prevent much possibility of large taxonomic groups being revised at all. Potentially more problematic (but unfortunately not supported with specific examples) is Mawson & Talent's implication that some of the new 'species' recognised by Bardashev et al. are in fact variants of other species and not phylogenetically distinct entities.

Bardashev & Weddige (2003) published a brief note in which they corrected the objective synonymy of Polygnathus and Costapolygnathus by publishing a new genus Eucostapolygnathus that they said "includes the same species as Costapolygnathus - except the species dubius". In a reply to Mawson & Talent's comments, Weddige (2005) defended Bardashev et al.'s (2002) use of a high number of taxa on the basis that the latter had been a 'pure form-taxonomic study'. Or, more extensively:

The genus subdivision proposed by BARDASHEV, WEDDIGE & ZIEGLER (2002) might be regarded as a subgeneric subdivision. In form-taxonomy, however, and the paper represents a pure form-taxonomic study, subgenera are not in usage. Because of the pure form-taxonomy, moreover, resp. because of a more or less subgeneric level of the proposed subdivision, a multielement reference, e. g. by suspect statistics, is not needed, for the first. Thus, a distinctive serious discussion has to focus on (form-) taxonomic characters, i. e. the valuation and order of the diagnostic characters as they are used for the generic subdivision by BARDASHEV et al.. Admittedly, a broadly splitted form spectrum, often including revolutionary ideas, is a hard diet. On the other hand, a well known unchanged form spectrum is a usual and therefore easy diet that, moreover, becomes much easier to digest when the spectrum, or parts of it, is furthermore lumped. The differentiation in “splitters” and “lumpers” is an inadequate simplification -- since the study by BARDASHEV et al. is not only a splitting because of different new taxa, it has rather more the character of a synthesis because of its search for phylogenetic lines by which single species were “lumped”). Thus, the study is a lumping on a quality level, higher than a taxonomic lumping that resigns to differentiate and searches for a conservative comfortable easy diet. Conservatives bloc progress, that is their job – and it would be a total misunderstanding that a SDS commission or a Working Party is entitled to condemn per joint decision (that could not be the target of a discussion!).

So in reply to accusation of being splitters, Weddige replies that no, they were lumpers, but his definition of 'lumping' can only be described as an Inigo Montoya moment. There is also the problem that Bardashev et al. was self-evidently not a purely form-taxonomy study. Form taxa are those based on morphological distinctions only that cannot be confirmed as phylogenetically distinct units - but Bardashev et al. (2002) presented their readers with no less than nine representations of preferred phylogenetic hypotheses, as well as specifically commenting on the descent of every one of the taxa they described. If these were only 'form taxa', then those 'lineages' are completely meaningless, and you, my friend, have just been treated to seventy-seven pages of intellectual masturbation.

REFERENCES

Bardashev, I., & K. Weddige. 2003. The invalid genus name Costapolygnathus Bardashev, Weddige & Ziegler 2002 and the new conodont genus Eucostapolygnathus. Senckenbergiana Lethaea 83 (1-2): 1-2.

Bardashev, I. A., K. Weddige & W. Ziegler. 2002. The phylomorphogenesis of some Early Devonian platform conodonts. Senckenbergiana Lethaea 82 (2): 375-451.

Dzik, J. 1991. Evolution of oral apparatuses in the conodont chordates. Acta Palaeontologica Polonica 36 (3): 265-323.

Lindström, M. 1974. The conodont apparatus as a food-gathering mechanism. Palaeontology 17 (4): 729-744.

Mawson, R., & J. A. Talent. 2003. Conodont faunas from sequences on or marginal to the Anakie Inlier (Central Queensland, Australia) in relation to Devonian transgressions. Bulletin of Geosciences 78 (4): 335-358.

Purnell, M. A., & P. C. J. Donoghue. 1997. Architecture and functional morphology of the skeletal apparatus of ozarkodinid conodonts. Philosophical Transactions of the Royal Society of London B 352: 1545-1564.

Sweet, W. C., & P. C. J. Donoghue. 2001. Conodonts: past, present, future. Journal of Paleontology 75 (6): 1174-1184.

Weddige, K. 2005. Contra Ruth Mawson’s critizising Bardashev, Weddige & Ziegler 2002, e.g. in SDS Newsletters 20 (2004). Subcommission on Devonian Stratigraphy Newsletter 21: 51-52.

Fungus and the Individual

noreply@blogger.com (Christopher Taylor) — Thu, 22 Oct 2009 03:38:00 +0000

After reading a post this morning over at Watching the World Wake Up that referred to fungi, I was reminded of the Individual Problem in biology - what exactly is an 'individual'? As I've had cause to say before, nature doesn't really like clear divisions, and the problem of individuality is a good example of something that seems clear and simple until one sits down and tries to actually define it.

Most of us would consider ourselves to be a separate individual, and probably only a single individual. But, of course, you are made up of large numbers of separate cells. In constrast, many organisms such as amoeboids and ciliates are separate individuals with only a single cell. Bridging the gap between these two are colonial unicellular organisms such as many choanoflagellates. Attempting to establish a clear line between what should be consider a colony of unicellular organisms and a single multicellular organism is a futile task as classically demonstrated by the example of sponges, made up of multiple distinct cell-types that are derived from a single ancestral zygote but retain the ability to function independently of the remainder of the sponge*. Amoeboid sponge cells may actually detach themselves from the base of the colony/individual and move off on short independent 'exploratory expeditions' before returning to the remainder of the sponge and re-integrating themselves**. The ability of sponges to re-assemble themselves after being divided into separate cells is also well-known (Galtsoff, 1923; if disassociated cells from two or more separate sponges are mixed together, they will re-assemble themselves back into separate sponges).

*Apparently, this is known as the "sorites paradox". 'Sorites' is Greek for 'something that is piled up', and the name relates to the question of how many grains of sand it takes for a cluster of grains to be considered a pile of sand. Hence, if I understand this correctly, a sorites problem applies to situations where you have two clearly distinct end-states, but no clear dividing line between them. Just to confuse matters, Sorites is also the name of a genus of foraminiferans.

**One small detail that you may not realise - as a result of this movement of amoeboid cells, the entire sponge is capable of very slow movement, a few millimetres over the course of a day.

Even if one tries to define the cell as individual, nature still has tricks up her sleeve. Multinucleate cells, for instance, can go through nuclear division without necessarily going through cell division, or go through cell division without going through nuclear division (anyone remember Trichosphaerium?) Hyphal or coenocytic organisms may be decidedly cavalier about whether or not they divide into separate cells. Even if the hyphae are transected by cell walls as in fungi, the walls may still have open pores that allow the free movement of nuclei between 'cells'. Plants also have connecting pores through cell walls called plasmodesmata; while plasmodesmata do not allow nuclear movement between cells, they do connect the cytoplasm of separate cells. Depending on how you chose to define a 'cell', it might be possible to regard an entire tree as a unicellular organism.

Things become even more complicated when you consider the possibility of separate 'individuals' within a single cell. For instance, there are intracellular parasites such as some red algae where free parasite nuclei are injected directly into the host cytoplasm without a cell membrane separating host and parasite. Fungi include some of the best examples of 'super-individual' cells, because of the ability of members of the Ascomycota and Basidiomycota (the two groups that include most macroscopic fungi) to form what is called a 'dikaryon'. As described by the Watcher in the post linked to at the top of this post, fertilisation in fungi occurs when two compatible lots of hyphae meet and fuse to exchange nuclei. However, unlike fertilisation in animals such as ourselves where the nuclei fuse right away to form zygotes, in fungi the two parent nuclei remain separate within the cytoplasm (fungi nuclei are normally haploid). Cell growth and division in the hypha continues as normal, with division of each of the separate nuclei maintaining the dikaryotic state in each of the new cells. It is these dikaryotic hyphae that make up the fruiting body, and fusion of the nuclei to form diploid zygotes does not happen until the actual point of spore production. So every mushroom you see represents the fusion of two separate parents, and contains (at least) two separate lines of nuclei. Is a mushroom one individual or two?

The dikaryon in basidiomycetes is maintained through cell division by the production of clamp connections, as shown in the figure above from here. While two nuclei move forward to become part of the new cell, one of the other nuclei moves into a side-branch and is re-injected into the old cell after cell division.

REFERENCES

Galtsoff, P. S. 1923. The amoeboid movement of dissociated sponge cells. Biological Bulletin 45 (3): 153-161.

Careful with that Spelling (Taxon of the Week: Barleeiidae)

noreply@blogger.com (Christopher Taylor) — Mon, 19 Oct 2009 03:43:00 +0000

The two millimetre long Barleeia angustata from Japan (assuming that this is not one of the "gastropods previously confused with Barleeia angustata" referred to in this abstract). Photo from here.

Seriously, watch it. There are some taxon names out there that seem to have been deliberately designed to provoke misspellings, and the double-e, double-i combination in Barleeiidae definitely puts it up there*. If Google Scholar search results are any indication, then publications using misspellings of Barleeiidae outnumber those using the correct spelling by a factor of ten. Barleeiidae and the type genus Barleeia derive their name from a George Barlee, a retired solicitor who regularly accompanied malacologist J. G. Jeffreys on collecting trips in the early 1800s (Fretter & Graham, 1978). The common name of "barley snails" is sometimes given to barleeiids; it looks more likely to be a mangling of the generic name rather than indicating any specific connection between barleeiids and barley.

*As well as providing a good example of the principle that taxonomic names are primarily designed to be written, not spoken. You can try saying that one aloud, but don't be surprised if passers-by think you've sprung a leak.

Barleeiidae are a family of marine gastropods found around the world. They belong to the Rissooidea (another tricky name to spell correctly), the same superfamily that includes the Caecidae. Unlike caecids, barleeiids have a gastropod-ordinary spired shell, usually about one and a half times as tall as wide. One noticeable feature that barleeiids do have in common with caecids, on the other hand, is their size - like caecids, barleeiids are minute, only about one or two millimetres tall. Species such as the north-west Atlantic Barleeia unifasciata live on macroalgae (i.e. seaweed), though their diet seems to be diatoms sitting on the weed more than the weed itself (Fernández et al., 1988). Barleeiid shells are smooth and mostly unornamented except for the protoconch (the very tip of the shell) with numerous fine spiral ridges (Fretter & Graham, 1978). The shell has an inner chitinous layer and the osphradium (the organ a marine gastropod smells with) is relatively large (Kabat & Hershler, 1993). Rissooids as a rule have separate males and females with the internally-fertilised females laying their eggs in lens-shaped capsules; in barleeiids and many other marine rissooids, the glands that secrete the capsule have a fairly basic structure, but in other rissooid families, particularly those including terrestrial and freshwater species, the oviduct glands become more complex.

Barleeia unifasciata. Photo from here.

The number of described species of barleeiids seems to be very small, possibly even less than twenty (see the Atlas of Living Australia listings, for instance), all but a few of which are included in Barleeia. The ALA listing (and other sources such as Wikipedia) includes the genus Amphithalamus in Barleeiidae, but Bouchet et al. (2005) placed that genus in the related but separate family Anabathridae. In view of their wide distribution, it seems certain that the small number of described barleiid species indicates a low level of study, and anyone willing to take on the study of such small animals would be bound to be rewarded with a wealth of new taxa.

REFERENCES

Bouchet, P., J.-P. Rocroi, J. Frýda, B. Hausdorf, W. Ponder, Á. Valdés & A. Warén. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1-2): 1-397.

Fernández, E., R. Anadón & C. Fernández. 1988. Life histories and growth of the gastropods Bittium reticulatum and Barleeia unifasciata inhabiting the seaweed Gelidium latifolium. Journal of Molluscan Studies 54: 119-129.

Fretter, V., & A. Graham. 1978. The prosobranch molluscs of Britain and Denmark. Part 4 - marine Rissoacea. Journal of Molluscan Studies Supplement 6.

Kabat, A. R., & R. Hershler. 1993. The prosobranch snail family Hydrobiidae (Gastropoda: Rissooidea): review of classification and supraspecific taxa. Smithsonian Contributions to Zoology 547.

Some Thoughts on How to Make Electronic Publication Work

noreply@blogger.com (Christopher Taylor) — Wed, 14 Oct 2009 03:49:00 +0000

"There is a cube of crystal here - though I can no longer tell you where -no larger than the ball of your thumb that contains more books than the library itself does. Though a harlot might dangle it from one ear for an ornament, there are not volumes enough in the world to counterweight the other."
--Gene Wolfe, The Shadow of the Torturer.

The ICZN is currently debating amendments to the Zoological Code that will formally accept the validity of names published in electronic publications (ICZN, 2008; if you're not familiar with the subject, I'd recommend reading the post just linked to before this one). Electronic publication raises a host of issues related to such matters as long-term availability and accessibility, but even an old curmudgeon like myself has to admit that it's gonna happen, whether we like it or not - in fact, it's already happening - and the question of whether or not to accept it has become more or less moot. The question, rather, is how to best respond to it.

I do have to apologise in advance for a few things I'm going to quote here without attribution that I know I've heard someone say somewhere, but I can't remember where or who. This post was partially inspired by Taylor (2009; that's Mike Taylor of SV-POW! fame, not me) and its rather snotty little title, but I wouldn't call it a direct reply. I'll also note that one of the interesting side effects of the debate on how to handle electronic publication is that it provides a much-needed impetus to tackle some of the neglected questions of how we handle printed publications.

Many of the complaints about electronic publication revolve around permanence. Supporters of electronic formats point out (and correctly so) that on-line publications* are both more readily and widely distributable than printed publications. However, for the purpose of taxonomy, we need to be thinking not only about current distribution, but also future distribution. Preservation of taxonomic works, theoretically, needs to be permanent (in the long term, of course, this is a problem for both printed and electronic works). It has been claimed that the large number of electronic copies floating around on people's private computers provides a guard against loss of an electronic publication, but this is not a sufficient guard in the majority of cases, because of the simple fact that not all organisms garner the same degree of attention. Taylor (2009) refers to the public interest around the publication of Darwinius masillae Franzen et al., 2009 - I mean, come on, it's a bloody monkey with its own bloody TV documentary, of course it raises a lot of interest. But taxonomy doesn't only concern fossil monkeys or honking great lizards, which are the other cases Mike cites. Yochelson (1969), working on Palaeozoic molluscs, estimated that the species description he wrote were "read by a worldwide audience that ranges from three to seven persons"**. This is not an audience that guarantees preservation. Also, there is a potential generational issue - when a researcher passes away, her copies of printed publications may be donated to a library and archived, but her hard-drive is likely to be thrown away or wiped.

*Including on-line versions of printed publications, which in a significant proportion of cases have become the effective primary version.

**Yochelson (1969) is a rather interesting publication for the current debate because he wrote it arguing that the ICZN should accept publications on microfilm. The more things change...

However, while permanent storage may be more of an issue for electronic media than printed media, it's one that is already being addressed, with the current proposals already including requirements for archival that, while arguably not perfect, are perhaps good enough for government work. The really major problem is not long-term availability, but long-term accessibility. To read a printed publication, I have simply to use my eyes, and for most of us they come pre-installed*. Reading an electronic publication, however, requires appropriate machinery and software. Claims that there will "always be a way to read PDF" are just hopelessly naïve, as are claims that we will be able to rely on conversion of electronic publications into newer formats as they gain prominence. Media will be converted if there is an immediate demand for their conversion, and the longer a given publication goes without being converted, the lower the chance that it will ever be converted (I'm pretty sure that a significant number of movies once available on VHS have not become available on DVD and probably never will). In the quote at the top of this post from a book set in our world's far-distant future, the librarian Ultan refers to what is obviously some sort of electronic storage device. What he fails to mention is that the technology to read the material stored on it no longer exists.

*Of course, it has to be in a language I can read, but that issue applies equally to electronic and printed media.

So electronic publications are not sufficiently reliable, but electronic publications are already here and only going to become more predominant. Are we doomed to confusion then? No, because I don't think that the means of evading the issues are really that difficult. The current code allows for the effective publication of electronic media if a permanent copy is deposited in a number of libraries on CD. The proposals in front of the ICZN include phasing out CD publication, and rightly so in my opinion - CD publication carries all the issues of accessibility associated with electronic media, without any of the advantages of online publication. But why not request the deposition of print-outs? That both allows for the validity of the electronic publication (with all its advantages of disseminability), while still maintaining the printed counterpart as a back-up.

Taylor (2009) points out that the current requirements for back-up deposition are vague and difficult to comply with. I would definitely agree that, if nothing else, they lead to something of a logical paradox in their current requirement that the publication itself include details of its own depositories. A simple reprint of the current requirements with "printed copy" substituted for CD would not help matters. But what about ZooBank? ZooBank is the proposed register of zoological names currently being developed. The current code does not require registration of names, but it is being considered and the electronic publication proposals include compulsary registration for electronically-published names at least (though as pointed out in the comments to the post linked to at the top of this one, if they're going to make it compulsary for some they might as well make it compulsary for all). A separate proposal that has been made that would make registration compulsary for all new names (Polaszek et al., 2005) allows a window of two years between publication and registration for a name to be validated*. Perhaps ZooBank could be expanded to also hold listings of archives of printed copies for electronic publications with, again, a two-year window to allow the authors/publishers to arrange the depositories and submit the info. Heck, the same thing could be done for names published in rare printed publications such as the journal Lansania that I've discussed previously.

*And it was this simple point that made yours truly no longer an avid opponent of registration. In a workable system, registration would have to come after publication, because the potential consequences of a name being published but not registered afterwards are minor compared to those of a name being registered but not published.

One potential complaint is that the printed version may not be identical to the electronic version. This would be particularly unavoidable if the electronic version includes such features as video that are not reproducible on paper. But for the purposes of taxonomy, what does the permanent record actually need? Name, type material, description/diagnosis. If the entire publication cannot be stored in printed form, then maybe allowances could be made for an abridged version containing the vital points to be deposited in its stead. Cantino et al. (2007) provides something of a precedent in botanical nomenclature (which currently excludes electronic publication) - a shorter, printed version of this work on plant phylogenetic nomenclature was published containing the essentials of definitions and such, while a longer electronic version allowed for more expansive discussion. So long as the two were not in direct conflict, then the existence of two versions does not actually pose a problem for nomenclatural purposes. For those wishing to guard against potential issues, perhaps a clause could be included in the code giving one of the versions priority over the other - I'd suggest something to the effect of the electronic version having priority so long as it remains available and accessible, because that's the version people are more likely to have access to in such cases.

Discuss.

REFERENCES

Cantino, P. D., J. A. Doyle, S. W. Graham, W. S. Judd, R. G. Olmstead, D. E. Soltis, P. S. Soltis & M. J. Donoghue. 2007. Towards a phylogenetic nomenclature of Tracheophyta. Taxon 56(3): E1-E44.

Franzen, J. L., P. D. Gingerich, J. Habersetzer, J. H. Hurum, W. von Koenigswald & B. H. Smith. 2009. Complete primate skeleton from the Middle Eocene of Messel in Germany: morphology and paleobiology. PLoS One 4 (5): e5723.

International Commission on Zoological Nomenclature. 2008. Proposed amendment of the International Code of Zoological Nomenclature to expand and refine methods of publication. Zootaxa 1908: 57-67.

Polaszek, A., M. Alonso-Zarazaga, P. Bouchet, D. J. Brothers, N. Evenhuis, F.-T. Krell, C. H. C. Lyal, A. Minelli, R. L. Pyle, N. J. Robinson, F. C. Thompson & J. van Tol. 2005. ZooBank: the open-access register for zoological taxonomy: Technical Discussion Paper. Bulletin of Zoological Nomenclature 62 (4).

Taylor, M. P. 2009. Electronic publication of nomenclatural acts is inevitable, and will be accepted by the taxonomic community with or without the endorsement of the Code. Bulletin of Zoological Nomenclature 66 (3): 205-214.

Yochelson, E. Y. 1969. Publication, microfilm, microcard, microfiche, and the International Code of Zoological Nomenclature. Systematic Zoology 18 (4): 476-480.

Crabs That Cannot Scratch Their Heads (Taxon of the Week: Parthenopidae)

noreply@blogger.com (Christopher Taylor) — Mon, 12 Oct 2009 03:51:00 +0000

An elbow crab amongst seaweed, showing both its long reach and well-developed camouflage. Photo from Wild Shores of Singapore.

Lift up one arm, and bend your elbow. Reach with your fingers to a point on your back, between your shoulder-blades. Scratch. Not only will that work wonders for any annoying tingle that you might have been feeling, but you have just demonstrated your superior flexibility to an elbow crab.

Crabs of the family Parthenopidae are found in tropical and subtropical coral reefs and shelly sea bottoms. Most species have bodies that are roughly triangular in shape, and often highly ornamented with lumps, bumps and spines (this ornamentation makes them very difficult to see among coral and rocks; it also encourages the growth of algae and other camouflaging organisms on the crab). They also usually have very large and long chelipeds (pincers), which make it easy to see how they got the name of 'elbow crabs'. The merus (the 'upper arm' part of the cheliped) is proportionally much longer than in many other crab families, giving parthenopids a real gorilla-ish look (I found one website that labelled a parthenopid of the genus Daldorfia as the "King Kong crab"). Despite their extraordinary size and length, however, the range of mobility of an elbow crab's chelipeds is limited, hence the point about back-scratching above. An elbow crab cannot reach the middle part of the top of its carapace.

Furtipodia petrosa, a rather adorable-looking parthenopid from Guam that resembles a sponge-covered rock. Furtipodia is also one of a number of parthenopids in which the walking legs are hidden by the carapace, improving the disguise. Photo from here.

This lack of cheliped mobility is one of the features distinguishing members of the Parthenopidae from the spider crabs of the Majidae, which have a broadly similar superficial appearance (Ng & McLay, 2003). Other distinct features of the family include the fusion of the third to fifth segments of the male abdomen* (Tan & Ng, 2007); also, while female majids have a high-domed abdomen that forms an entirely enclosed brood chamber for her eggs, the parthenopid female's abdomen does not entirely seal the eggs away from the outside world. The similar adult appearance of Parthenopidae and Majidae, with their triangular bodies and pointed snouts, lead most early authors to regard them as closely related, but the similarities are now thought to be convergent. The larvae of parthenopids are more similar to those of other families than majids (Yang, 1971), while phylogenetic studies do not support their association (Brösing, 2008).

Normal parthenopids are remarkable enough, but Lambrachaeus ramifer looks like something out of a Japanese video game (making it appropriate that I found this photo on a Japanese website). This individual is a female carrying eggs - they're the orange mass on her underside.

The subfamilial classification of Parthenopidae was reviewed by Tan & Ng (2007) who recognised only two subfamilies of elbow crabs, the Parthenopinae and Daldorfiinae (earlier authors recognised more - some have been moved to other families, others have been synonymised). The two subfamilies are distinguished by only a single character, the relative length of the antennal segments, and a more formal analysis is still required to test their distinction. A separate subfamily had previously been recognised for the very distinctive Indo-Pacific species Lambrachaeus ramifer which has the front of the carapace extended forward into a long neck (Ng & McLay, 2003), but Tan & Ng (2007) placed this species in Parthenopinae, noting that it had been separated on the basis of its own peculiar autapomorphies rather than by lack of the features of other subfamilies.

*If you don't know where to find the abdomen of a crab, then look at the underside of one the next time you're able to. The much reduced abdomen is turned forwards and held on the underside of the cephalothorax. In males, it is a small, narrow segmented strip. In females, it is much larger and broader, and is used to hold her eggs.

REFERENCES

Brösing, A. 2008. A reconstruction of an evolutionary scenario for the Brachyura (Crustacea) in the context of the Cretaceous-Tertiary boundary. Crustaceana 81 (3): 271-287.

Ng, P. K. L., & C. L. McLay. 2003. On the systematic position of Lambrachaeus Alcock, 1895 (Brachyura, Parthenopidae). Crustaceana 76 (8): 897-915.

Tan, S. H., & P. K. L. Ng. 2007. Descriptions of new genera from the subfamily Parthenopinae (Crustacea: Decapoda: Brachyura: Parthenopidae). Raffles Bulletin of Zoology Supplement 16: 95-119.

Yang, W. T. 1971. The larval and postlarval development of Parthenope serrata reared in the laboratory and the systematic position of the Parthenopinae (Crustacea, Brachyura). Biological Bulletin 140: 166-189.

If They Only Wood (Taxon of the Week: Diaporthales)

noreply@blogger.com (Christopher Taylor) — Sun, 04 Oct 2009 06:50:00 +0000

Perithecia (fruiting bodies) of Cryphonectria cubensis, the cause of eucalyptus canker. Photo by Edward Barnard.

Most people, when they think of fungi, will think of mushrooms. However, the majority of fungi do not produce such large and obvious structures as mushrooms; the majority of fungi are microscopic decomposers, whose minute fruiting bodies would be easily overlooked by those not looking for them. But tiny as these organisms are, they can have a significant effect on your life.

The Diaporthales are one order of these microfungi. They are a well-defined order of ascomycetes with brown or black perithecia (almost entirely enclosed fruiting bodies with only a single pore at one end and the spores produced inside) submerged either within a stroma (mass of hyphal tissue) or in the surrounding substrate on which they are growing (Rossmann et al., 2007). In many Diaporthales, the opening pore of the perithecia is on a long neck that may or may not also be submerged; it is the combination of round perithecium and elongate neck that lead the authors of one recently-described genus to dub it Lollipopaia (Inderbitzin & Berbee, 2001).

Pycnidia of Cryphonectria parasitica protruding from chestnut bark. Pycnidia resemble perithecia, but differ in containing asexually- rather than sexually-produced spores. Photo from here.

Most Diaporthales are decomposers of rotting wood. As such, they rarely come to humanity's attention, though it probably wouldn't take us long to notice if they disappeared. A small but significant number of Diaporthales, however, have earned a great deal of attention from humans because, while they grow on wood just like their relatives, they don't have the courtesy to wait for the tree to die first. The most famous (or notorious, depending on your preferred choice of adjectives) of Diaporthales is undoubtedly Cryphonectria parasitica, the cause of chestnut blight and famed as the bane of the American chestnut, C. dentata. According to Wikipedia, C. dentata may have made up as much as a quarter of the forest in the Appalachian region of eastern North America prior to the arrival of chestnut blight around 1905; by 1940, it was almost extinct. To this day, the position of the American chestnut across most of its original range remains tenuous; complete extinction has been staved off by the chestnut's ability to produce subsidiary shoots from its base, meaning that a number of trees survive despite being reduced to the central boles. However, complete regrowth is likewise prevented by the fungus attacking any new shoots before they achieve significant growth. Meanwhile, attempts to breed blight-resistant strains of American chestnut are hampered by the tree's slow growth rate.

Three views of American chestnut (Castanea dentata). On the left, American chestnut trees as they could still be found in 1910. In the centre, American chestnut as it survives today - an understorey regenerating shrub, prevented from reaching full growth by the inevitable onset of blight. On the right, the intermediary stage in a grown chestnut felled by the fungus. Images from Ellison et al. (2005).

When chestnut blight was recorded in European chestnut trees (Castanea sativa) in Italy in 1938, people expected a repeat of the American experience. And at first, that was almost exactly what happened - chestnut blight spread rapidly through western Europe, slowed only by the more scattered distribution of its host (C. sativa was not originally native to most parts of Europe, but introduced by the Romans; as a result, it does not form continuous forests in Europe as C. dentata did in America, but is largely only found where it has been deliberately planted by humans). However, during the 1950s and 1960s, reports started coming in of stands of chestnuts that appeared to be coping surprisingly well despite the obvious presence of blight (Heiniger & Rigling, 1994), with the damage from the blight extending only a short way into the wood (as it does in the Asian chestnut Castanea crenata, the original host of the fungus). What was more, when fungal hyphae from these wimpier infections were transplanted into further chestnut trees amongst more normal raging infections, the more virulent infections began to heal. The reduced virulence turns out to be due to a virus infecting the fungus - the disease being cured by a disease of its own. The spread of reduced virulence among chestnut blight in Europe has massively reduced the European epidemic. Attempts to implement the same cure in North America, however, have mostly resulted in failure (Milgroom & Cortesi, 2004). Transmission of reduced virulence between fungal colonies is slow and ineffecient, and in most cases seems to require direct human intervention to be truly effective. While this direct intervention is feasible with the more scattered European chestnut, it offers little hope of restoring the prior forests of American chestnut.

Other species of Diaporthales cause diseases in other crop trees and plants (including butternut canker caused by Sirococcus clavigignenti-juglandacearum, which I'm sure is a terrible thing to be afflicted by, even if it does sound like the name of some sort of confectionary). Dogwood anthracnose is caused by Discula destructiva, recently shown to be an anamorphic (asexual) member of the Diaporthales. Cytospora species attack Eucalyptus, while Greeneria uvicola causes bitter rot in grapes. If you feel enticed to explore the systematics and characteristics of the various subgroups of Diaporthales, there's an impressively detailed coverage on the U.S. Department of Agriculture's Diaporthales page, including a big interactive tree where clicking on a clade brings up descriptions and images to help you while away the hours.

REFERENCES

Ellison, A. M., M. S. Bank, B. D. Clinton, E. A. Colburn, K. Elliott, C. R. Ford, D. R. Foster, B. D. Kloeppel, J. D. Knoepp, G. M. Lovett, J. Mohan, D. A. Orwig, N. L. Rodenhouse, W. V. Sobczak, K. A. Stinson, J. K. Stone, C. M. Swan, J. Thompson, B. Von Holle & J. R. Webster. 2005. Loss of foundation species: consequences for the structure and dynamics of forested ecosystems. Frontiers in Ecology and the Environment 3 (9): 479-486.

Heiniger, U., & D. Rigling. 1994. Biological control of chestnut blight in Europe. Annual Review of Phytopathology 32: 581-599.

Inderbitzin, P., & M. L. Berbee. 2001. Lollipopaia minuta from Thailand, a new genus and species of the Diaporthales (Ascomycetes, Fungi) based on morphological and molecular data. Canadian Journal of Botany 79: 1099-1106.

Milgroom, M. G., & P. Cortesi. 2004. Biological control of chestnut blight with hypovirulence: a critical analysis. Annual Review of Phytopathology 42: 311-338.

Rossmann, A. Y., D. F. Farr & L. A. Castlebury. 2007. A review of the phylogeny and biology of the Diaporthales. Mycoscience 48: 135-144.

Secret Identities

noreply@blogger.com (Christopher Taylor) — Sat, 03 Oct 2009 02:31:00 +0000

A couple of days ago, I asked if you could guess the identity of organisms previously placed in quite different taxonomic positions from the ones they occupy now (if you haven't done it yet, click on the link and have a go before you come back here). And here are the answers:

1. Vorticella cincta Müller 1773 = Peridinium cinctum (photo by Kate Howell).

Psi got this one, but her assumption that a dinoflagellate was being mistaken for a ciliate is not entirely accurate. Vorticella cincta was one of the very first two dinoflagellates to be named; both were described as ciliates. Dinoflagellates possess two long cilia (or flagella, if you prefer), and carry one of the cilia wrapped around themselves in a groove (it is the movement of this wrapped cilium that gives dinoflagellates their characteristic twirling movement*). Early microscopists, who could probably see the movement in the groove but not make out the actual cilium, thought that the groove was a band of small individual cilia as found in ciliates.

*Come to think of it, maybe that's why dinoflagellates do everything so strangely - their constant spinning has left them so disoriented that they can no longer tell good sense from bad.

2. Helix smaragdus Martyn 1784 = Turbo smaragdus (photo by Graham Bould).

Turbo smaragdus is the ultra-common cat's eye shell of New Zealand (the common name refers to the pattern of the operculum). Early mollusc systematists tended to use a very small number of large genera; indeed, I've occasionally been driven to wonder if some of them recognised only two genera of gastropods - Helix for everything with a shell, Limax for everything without. Molluscs are one of the worst groups of organisms (ferns are probably the other) for what I've dubbed the "Evil Old Genus" effect. Evil Old Genera are those that have included a very large number of species over their history, most of which have since been placed in other genera, making synonymies and homonymies an absolute nightmare to keep track of. (The most evil of Evil Old Genera, perhaps, is the neogastropod Pleurotoma; Pleurotoma has been used for hundreds of species, but what makes it really ghastly is that Pleurotoma has the exact same type species as Turris, an older name by a year, so Pleurotoma is not even a valid genus.) The main reason for the initial conservatism of molluscan taxonomy was that it was then based almost entirely on shell morphology only; it would not be until later that malacologists decided that it might be interesting to look at the squashy bits inside the shell as well. True Helix as currently recognised is a terrestrial pulmonate snail; Turbo belongs to a very different group of gastropods, the marine vetigastropods. For comparison, the two are probably less closely related than you are to a goldfish.

3. Nautilus radicula Linnaeus 1758 = Nodosaria radicula (photo of Nodosaria bacillum from here).

Linnaeus' original concept of Nautilus actually included more foraminiferans than molluscs. In the eyes of many early researchers, the resemblance in structure of the foram shell divided into chambers to the shell of a microscopic cephalopod indicated that that was just what they were. It took until the 1800s for the fundamentally different anatomy of forams to be recognised.

4. Phalangium cancroides (Linnaeus 1758) (originally Acarus cancroides) = Chelifer cancroides (photo from here).

This is another case of a genus name originally referring to a much broader concept than today; Linnaeus used the name Phalangium for all arachnids with a segmented abdomen but without the sting of Scorpio. Not just harvestmen, but pseudoscorpions, sun spiders, whip scorpions and amblypygids were placed in Phalangium.

5. Cancer pulex Linnaeus 1758 = Gammarus pulex (photo from here).

Cancer was used Linnaeus not just for crabs, but for pretty much all crustaceans.

6. Asterias bifida Pennant 1777 = the crinoid Antedon bifida (photo from here).

7. Holothuria priapus Linnaeus 1767 = Priapulus caudatus (photo by Marko Herrmann).

To be honest, I'm not sure why this one doesn't still go by Linnaeus' original (perhaps overly descriptive for those of a sensitive nature) name of Priapus humanus ("human dick"). The other species in Linnaeus' Priapus, Priapus equinus ("horse dick"), is a sea anemone. And if you're surprised that Linnaeus should be so crude, try looking up the story behind his name for the marine worm Aphrodita.

8. Gasterosteus volitans Linnaeus 1758 = Pterois volitans (photo from here).

Linnaeus has proved to be a little more prescient in this case that he is usually given credit for. After being placed in separate orders for a great many years, phylogenetic studies are now indicating that the Gasterosteidae (sticklebacks) are in fact nested among the former Scorpaeniformes, of which the lionfish is a member. And while I'm at it, I may as well remind of my earlier reference to observations of lionfish evolution in action.

9. Vultur fulvus Hablizl 1783 = Gyps fulvus (photo by Aka).

Though you could well argue that this one has gone nowhere. Linnaeus included species of both New World and Old World vultures in the genus Vultur. When it was later recognised that these two groups of birds were in fact not closely related, authors disagreed over whether the name Vultur should be used for the New World or the Old World vultures. In the end, those who used it for New World vultures won out almost by default.

10. Upupa eremita Linnaeus 1758 = Geronticus eremitus (photo by clkayleib).

Bonus points go to Lars Dietz, who not only successfully identified this species but managed to beat me at my own game by telling me the back-story that I didn't even know myself. According to Lars, Linnaeus himself had never actually seen one of these birds, and was describing it from its reputation.

11. Myrmecophaga striata Shaw 1800 = Nasua nasua (photo by Matthias Kabel).

Shaw's identification of this animal as an anteater rather than a carnivoran may be related to the fact that, again, his description seems to have been based on someone else's (specifically, the Comte de Buffon's) illustration of a specimen rather than on the specimen itself. It doesn't help that, if Shaw's illustration is any indication, the specimen was pretty poorly mounted. On the other hand, Shaw's concept of Myrmecophaga also included the aardvark and the echidna, so it was already rather broad.

12. Lemur simiasciurus Schreber 1774 = Potos flavus (photo from here.

Or maybe not. Schreber seems to have used the names Lemur flavus and Lemur simiasciurus ("monkey-squirrel lemur" - great name, no?) as alternative labels for the same species, the animal now known as the kinkajou (a South American carnivoran, not a lemur). And in response to Neil's incredulity that a kinkajou could be identified as a lemur - it's arboreal, it has a curly tail, how much more like a lemur could you want it to be? But to complicate matters, Schreber's supposed illustration of "Lemur simiasciurus" is not a kinkajou, but an actual lemur (Lemur mongoz). Authors have differed as to whether L. simiasciurus was supposed to apply to the kinkajou or the lemur (with perhaps the majority supporting the former, if only by default), but as the name is unlikely to return to use in the either case the question is largely academic anyway.

13. Mus canguru Statius Müller 1776 = probably Macropus giganteus (photo by Di Paice).

Among the specimens Joseph Banks carried back from his stint in Australia as botanist to Captain Cook was one that he described as a "mouse" or "jerbua" even though it differed from the usual run of mice in weighing about eighty pounds. This was the animal that Statius Müller was to refer to as _Mus canguru_ (the popular story that the word "kangaroo" was actually Aboriginal for "I don't know what it is" or "I don't understand what you're saying" seems to be a myth, probably arising from confusion when British colonists tried to use the word in speaking to all Aboriginals even though they wouldn't have recognised the word unless they happened to speak Guugu-Yimidhirr*). Most authors have believed that Banks' "kanguru" was a specimen of Macropus giganteus, the eastern grey kangaroo, and many authors used Macropus canguru as the valid name for that species. Unfortunately, Banks' original description is not detailed enough to be certain of the identity of Mus canguru - it might refer to another Macropus species - and the ICZN eventually suppressed the name in favour of M. giganteus.

*Ellis (2001) refers to a particularly brilliant example of this confusion in a report of Sydney Cove Aboriginals referring to European cattle as "kangooroo", apparently because they thought that it was an English word.

14. Lutra minima Zimmermann 1780 = Chironectes minimus (photo from here).

Not a semi-aquatic carnivoran, but a semi-aquatic marsupial.

15. Viverra cancrivora Brongniart 1792 - This was the only entry that no-one identified correctly. Many of you thought that it might be Procyon cancrivorus, the crab-eating racoon. Nope. Cabrera (1957) listed this name in the synonymy of:

Cerdocyon thous (photo by Rhett Butler).

Not very civet-like, is it?

16. Limax lanceolatus = Branchiostoma lanceolatum (photo from here.

Nor is a lancelet much like a slug.

REFERENCES

Cabrera, A. 1957. Catalogo de los mamiferos de America del Sur. I (Metatheria - Unguiculata - Carnivora). Revista del Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” e Instituto Nacional de Investigacion de Las Ciencias Naturales, Ciencias Zoológicas 4 (1): 1-307.

Ellis, M. 2001. Tails of Wonder: constructions of the kangaroo in late eighteenth-century scientific discourse. In Science and Exploration in the Pacific: European Voyages to the Southern Oceans in the Eighteenth Century (M. Lincoln, ed.) pp. 163-182. Boydell & Brewer.

Taxonomy Trivia Quiz #2: You've Come a Long Way, Baby

noreply@blogger.com (Christopher Taylor) — Thu, 01 Oct 2009 04:19:00 +0000

If there are any of you who remember the last time I presented a quiz - don't worry, this one will probably be easier. But first, a little background (which may be familiar to some of you):

In 1887, Othniel Charles Marsh described a pair of large fossil horns as Bison alticornis, placing them in the same genus as the modern bison. As it turned out, the horns were not from a bison, they were from a dinosaur, either Triceratops or a close relative (the 'Bison' alticornis remains are not extensive enough to be sure). 'Bison' alticornis is just one of many cases of species originally assigned to genera to which they are no longer regarded as closely related. In some cases, such as the example I've just given, the original author did not have the material available that would have allowed a more accurate placement (ceratopsid fossils combining both dinosaurian characteristics and horns would not be described until a year later, by Marsh himself; at the time he described the alticornis horns, the possibility that they might have come from some sort of gigantic lizard probably never entered the equation). Sometimes, the concept associated with the genus name was simply far broader than its present circumscription (Linnaeus' original concept of Vespertilio, for instance, covered all bats). And sometimes, the characters regarded as defining a genus were different from the characters used today (Linnaeus' Falco was defined as carnivorous birds with a feathered head, hooked beak and without a covering of bristles at the base of the beak; it therefore included members of modern Accipitridae as well as Falconidae).

Below are fifteen examples of species names that are now placed some distance taxonomically from their original (or early) genera. Some are still recognised as valid species, some have been synonymised with other species. What I want you to do is tell me what these animals really are:

1. The 'ciliate' Vorticella cinctum.

2. The 'snail' Helix smaragdus.

3. The 'nautilus' Nautilus radicula.

4. The 'harvestman' Phalangium cancroides.

5. The 'crab' Cancer pulex.

6. The 'starfish' Asterias bifida.

7. The 'sea cucumber' Holothuria priapus.

8. The 'stickleback' Gasterosteus volitans.

9. The 'condor' Vultur fulvus.

10. The 'hoopoe' Upupa eremita.

11. The 'anteater' Myrmecophaga striata.

12. The 'lemur' Lemur simiasciurus.

13. The 'mouse' Mus canguru.

14. The 'otter' Lutra minima.

15. The 'civet' Viverra cancrivora.

And as a bonus point:

16. The 'slug' Limax lanceolatus.

Winners win the right to say "I won".

Picture Credits:

Vorticella used before, but original source page appears to have vanished.
Helix pomatia by Janek Pfeiffer.
Nautilus from here.
Phalangium opilio from Morten Hansen.
Cancer productus by Dave Cowles.
Asterias forbesi from here.
Holothuria edulis from here.
Gasterosteus aculeatus from here.
Vultur gryphus from here.
Upupa epops by Claudio Torresani.
Myrmecophaga tridactyla by Christopher Reiger.
Lemur catta from here.
Mus musculus from here.
Lutra lutra by David Pape.
Viverra zibetha by Robert Sterndale.
Limax maximus by Matthew Bulbert.

&^%$ Americans, Think They Own the Internet....

noreply@blogger.com (Christopher Taylor) — Thu, 01 Oct 2009 02:27:00 +0000

Does anyone out there have a pdf of Case's (1907) "Revision of the Pelycosauria of North America"? Archive.org claims that Google Books has the pdf available for free (and it's out of copyright), but it appears to be one of the apparently-not-insignificant number of books that Google is only making available in the USA, because I can't access it.

Thank you to anyone that's able to help.

A South American Paradox (Taxon of the Week: Sellocharis)

noreply@blogger.com (Christopher Taylor) — Mon, 28 Sep 2009 06:52:00 +0000

Aspects of Sellocharis paradoxa (Papilionaceae) as illustrated by Polhill (1976): "1, habit; 2, node with stem cut away to show leaf-arrangement; 3, flower; 4, calyx, opened out; 5, standard; 6, wing; 7, keel; 8, stamens, spread out; 9, anthers; 10, pistil; 11, same with ovary-wall cut away to show ovules".

A brief entry today, because Taxon of the Week this week is a bit of a mystery. The southern Brazilian leguminous subshrub Sellocharis paradoxa was first described in 1889, but for a very long time was known solely from the original isotypes*. It has only been rediscovered in scrubby grasslands and rockfields of the Brazilian state of Rio Grande do Sul within the last ten years or so (Conterato et al., 2007). Without having seen the original description, I can't tell you for certain what earned Sellocharis the name of 'paradoxa', but I suspect it was probably the unique arrangement of its leaves. As you can see in the figure above**, S. paradoxa has its leaves arranged in regular whorls of five to seven. The individual "leaves" are more similar to the leaflets of other leguminous plants, and Polhill (1976) tentatively suggested that that might be what they were - that instead of having whorls of six leaves, S. paradoxa might have only a single leaf that had lost its basal stalk so completely that it had merged with the main stem.

*For the non-botanists among you, "isotypes" are two or more type specimens that have been taken from the same original individual, such as two branches from a single tree.

**Now possibly the only depiction of Sellocharis available freely online. Not that I'm bragging or anything (especially considering I just scanned it out of the original book).

As befits its unusual morphology, the relationships of Sellocharis paradoxa are similarly mysterious. The most similar genus is Anarthrophyllum, a genus of Andean 'cushion plants' in which the stipules of the often trifoliate leaves surround the stem, often forming a sheath, and most authors seem to have assumed a relationship between the two genera. Flower morphology and the presence of α-pyridone alkaloids in Anarthrophyllum suggest a position in the Genisteae, the tribe including brooms, gorse and lupins, which I described in a previous post. Within the Genisteae, the flowers of Anarthrophyllum and Sellocharis are most similar to those of the basal Argyrolobium group. A large-scale molecular analysis of Papilionaceae placed Anarthrophyllum as sister to the clade of Lupinus and Genistinae (Wojciechowski et al., 2004), which is consistent with the previously suggested position of the Argyrolobium group (Ainouche et al., 2003) though no other members of the group were included in the later analysis. However, Polhill (1976) noted that, if one interprets the 'leaves' of Sellocharis as leaflets of a single divided leaf, then they bear a certain resemblance to the leaves of lupins and may indicate a relationship to that genus instead.

A genistean position for Sellocharis and Anarthrophyllum is still not un-problematic. As described in the previous post, the Genisteae is a primarily Old World lineage. Lupinus is the only other genus of Genisteae found in the Americas, and as it is found in both the Old and New Worlds it could be a later invader of the latter. Nevertheless, other genera of the Argyrolobium group are found in southern Africa, and the ancestors of Sellocharis may have come from there as other organisms are known to have done (the ancestors of the New World monkeys being perhaps the most famous example). Also potentially problematic is that the number and morphology of chromosomes in Sellocharis is very distinct from those of any other Genisteae; however, the authors who described Sellocharis' karyotype (Conterato et al., 2007) only referred to its differences from Genisteae without comparing it to members of other tribes. Hopefully, now that Sellocharis paradoxa has been re-found, more progress can be made on establishing just what it is.

REFERENCES

Ainouche, A., R. J. Bayer, P. Cubas & M.-T. Misset. 2003. Phylogenetic relationships within tribe Genisteae (Papilionoideae) with special reference to genus Ulex. In Advances in Legume Systematics part 10, Higher Level Systematics (B. B. Klitgaard & A. Bruneau, eds.) pp. 239-252. Royal Botanic Gardens: Kew.

Conterato, I. F., S. T. Sfoggia Miotto & M. T. Schifino-Wittman. 2007. Chromosome number, karyotype, and taxonomic considerations on the enigmatic Sellocharis paradoxa Taubert (Leguminosae, Papilionoideae, Genisteae). Botanical Journal of the Linnean Society 155 (2): 223-226.

Polhill, R. M. 1976. Genisteae (Adans.) Benth. and related tribes (Leguminosae). Botanical Systematics 1: 143 - 368.

Wojciechowski, M. F., M. Lavin & M. J. Sanderson. 2004. A phylogeny of legumes (Leguminosae) based on analysis of the plastid matK gene resolves many well-supported subclades within the family. American Journal of Botany 91: 1846-1862.

The Voice of the Turtle (Taxon of the Week: Streptopelia)

noreply@blogger.com (Christopher Taylor) — Mon, 21 Sep 2009 03:51:00 +0000

Eurasian collared dove Streptopelia decaocto, the most widespread Streptopelia species in Europe. Photo by Rovdyr.

The bird genus Streptopelia comprises the turtledoves or collared doves - thirteen to seventeen species (depending on preferred generic boundaries) of medium-sized, generally pinkish birds that have long garnered human admiration due to their attractive appearance and cooing vocalisations. The name "turtledove" is derived from the Latin turtur, which is itself an imitation of the sound made by the doves. The calls of different species of turtledoves are distinct, and often play a significant part in their identification (Slabbekoorn et al., 1999). Streptopelia doves are native to Africa and the warmer parts of Asia and Europe, but a number of species have been introduced to other parts of the world. Here in Perth, for instance, the laughing dove S. senegalensis and the spotted dove S. chinensis are both abundant (the former particularly so), while S. chinensis is also a successful exotic in Auckland back in New Zealand. Also widely introduced is the African collared dove or Barbary dove Streptopelia risoria*.

*The Barbary dove ("S. risoria") is the domesticated form of the African collared dove ("S. roseogrisea"), and most modern authors no longer regard the two as specifically distinct. S. risoria Linnaeus, 1758 has priority over S. roseogrisea Sundevall, 1857. However, it has become common practice for the name based on a "wild" taxon to be given preference over one based on a domestic taxon because of the often complicated nature of taxonomic concepts in relation to domesticated animals (Gentry et al., 2004), and so many authors have preferred to use S. roseogrisea for the combined taxon. A recent proposal to formalise this situation was turned down by the ICZN (ICZN, 2008), leaving S. risoria as the valid name for this species.

The Madagascar turtle dove Streptopelia picturata (aka Nesoenas picturata). Phylogenetic analysis indicates that this species is closely related to the pink pigeon Nesoenas mayeri (=Streptopelia mayeri) of Mauritius. Though distinct morphologically, the two species have very similar vocalisations. Photo from here.

In the past, Columbidae (pigeons and doves) have mostly been divided between two subfamilies, the Columbinae (standard columbids) and Treroninae (fruit-pigeons and fruit-doves), with separate monogeneric subfamilies for the morphologically distinctive genera Goura and Didunculus (and sometimes Otidiphaps) and a separate family Raphidae for the extinct dodo Raphus cucullatus and solitaire Pezophaps solitaria. This arrangement, never particularly sturdy at the best of times, has been blown out of the water by recent analyses (Pereira et al., 2007), which render the traditional Columbinae paraphyletic to the other subfamilies and Raphidae while the Treroninae becomes polyphyletic. To date, no-one has formally proposed a revised subfamilial classification of Columbidae, though Pereira et al. (2007) did recognise three well-supported clades in the family which they called simply A, B and C*.

*Because I have the comfort of knowing that no-one is going to take any notice of me in this matter, I can reveal that if we were to recognise these three clades as a subfamily each, they would become respectively Columbinae, Claravinae and Raphinae (going by the dates reported in Bock, 1994), and I find a certain pleasant irony in the idea that Raphinae would be the largest of the three.

The collared dove Streptopelia chinensis (=Stigmatopelia chinensis). Originally native to eastern Asia, the collared dove has been widely introduced elsewhere in the world. Photo by Charles Lam.

Whatever the eventual division of the family, Streptopelia will almost certainly remain a part of Columbinae, as it is the most closely related genus to Columba. Molecular analysis of fourteen of the sixteen species generally included in Streptopelia by Johnson et al. (2001) identified three main clades in the genus - a large clade containing the majority of species, a clade uniting S. chinensis and S. senegalensis, and a clade containing the Madagascan S. picturata and the pink dove Nesoenas mayeri of Mauritius. This three-part division is also reasonably consistent with morphological and vocal distinctions within the genus. The two smaller clades were in turn sister to each other, but the monophyly of Streptopelia as a whole was not proven; depending on the chosen method of analysis, either Streptopelia was monophyletic (the maximum likelihood results) or the main Streptopelia clade was sister to a clade containing Old World Columba and the two smaller clades (the maximum parsimony results). New World 'Columba' species were the sister clade to Streptopelia plus Old World Columba whatever the method; their recognition as a separate genus Patagioenas was proposed. Johnson et al. (2001) chose to retain Streptopelia in its previous circumscription, but with 'Nesoenas' mayeri also included. In contrast, Cheke (2005) suggested restricting Streptopelia to the main clade and recognising the smaller clades as separate genera Nesoenas (for mayeri and picturata) and Stigmatopelia (for chinensis and senegalensis). Johnson et al.'s (2001) system has the advantage of minimising the number of name changes involved; Cheke's (2005) system is potentially more robust to the uncertain monophyly of the broader Streptopelia; only time will tell which gains the greater popularity.

REFERENCES

Bock, W. J. 1994. History and nomenclature of avian family-group names. Bulletin of the American Museum of Natural History 222: 1-281.

Cheke, A. S. 2005. Naming segregates from the Columba–Streptopelia pigeons following DNA studies on phylogeny. Bulletin of the British Ornithologists' Club 125 (4): 293-295.

Gentry, A., J. Clutton-Brock & C. P. Groves. 2004. The naming of wild animal species and their domestic derivatives. Journal of Archaeological Science 31: 645-651.

ICZN. 2008. Opinion 2215: Streptopelia risoria (Linnaeus, 1758) (Aves, Columbidae): priority maintained. Bulletin of Zoological Nomenclature 65 (4).

Johnson, K. P., S. de Kort, K. Dinwoodey, A. C. Mateman, C. ten Cate, C. M. Lessells & D. H. Clayton. 2001. A molecular phylogeny of the dove genera Streptopelia and Columba. Auk 118 (4): 874-887.

Pereira, S. L., K. P. Johnson, D. H. Clayton & A. J. Baker. 2007. Mitochondrial and nuclear DNA sequences support a Cretaceous origin of Columbiformes and a dispersal-driven radiation in the Paleogene. Systematic Biology 56 (4): 656-672.

Slabbekoorn, H., S. de Kort & C. ten Cate. 1999. Comparative analysis of perch-coo vocalizations in Streptopelia doves. Auk 116 (3): 737-748.

Archamoebae: The Apogee (or Nadir) of Amoebozoan Evolution

noreply@blogger.com (Christopher Taylor) — Fri, 18 Sep 2009 03:46:00 +0000

Mastigamoeba aspera, the type species of the mastigamoebids. Photo by Josef Brief.

There's just one group of amoebozoans left for me to cover: the Archamoebae. Among Amoebozoa, the Archamoebae are easily distinguishable by one significant feature - they lack mitochondria. Mitochondria are also absent in Breviata (which was initially identified as an archamoeba as a result), but Breviata has double basal bodies attached to the cilium unlike the single basal body of Archamoebae (Walker et al., 2006). Members of the Archamoebae are either freshwater amoeboflagellates or non-ciliate animal endosymbionts. Because the Archamoebae are primarily defined by a character absence some authors have suggested that their monophyly is suspect, but molecular analyses support their recognition. The lack of mitochondria also lead to Archamoebae being one of the four groups of protists (along with the Diplomonadida, Microsporidia and Parabasalia) that were grouped together as the "Archezoa", and suggested to have diverged from other eukaryotes prior to the origin of mitochondria. The archezoan hypothesis began to fall from favour in the latter half of the 1990s as relationships were proposed between various 'archezoans' and specific groups of mitochondriate protists, such as between Archamoebae and other amoebozoans. Putative mitochondrion-derived organelles such as mitosomes and/or hydrogenosomes have now been identified from most Archamoebae (Walker et al., 2001; Gill et al., 2007).

Molecular data supports the division of Archamoebae into two clades, the Mastigamoebida and Pelobiontida (Cavalier-Smith et al., 2004). Production of pseudopodia in Mastigamoebida is eruptive (Walker et al., 2001), which you may recall is not the usual condition for amoebozoans (other than Archamoebae, eruptive pseudopodium is also found in Leptomyxida). Free-living mastigamoebids are ciliate for at least part of their life cycle, and movement is generally by means of the cilium or by gliding rather than by pseudopodium production. Mastigamoebids may or may not be multinucleate, and the cilium is usually connected to the nucleus. Taxonomy of the free-living amoeboflagellate mastigamoebids is in something of a state of flux - three genera have been distinguished, Mastigamoeba, Phreatamoeba and Mastigella, but opinions differ as to whether the latter two should be distinguished from the first. Phreatamoeba balamuthi has been placed as a separate genus because of its more complex life-cycle alternating between amoeboid and amoeboflagellate stages, with the amoeboid stage predominant, but the flagellate stage is otherwise not distinguishable from Mastigamoeba. Mastigella has been distinguished based on the absence of a connection between the cilium and the nucleus, but the presence or absence of such a connection can be difficult to distinguish in taxa where the connection is very fine (Walker et al., 2001). Part of the problem lies in the genus Mastigamoeba itself - Mastigamoeba contains about forty species of which some are very distinct from each other but many (including the type species) are insufficiently studied. When more of the Mastigamoeba species are studied it may lead to the genus' subdivision.

The giant micro-aerobic amoeboid Pelomyxa palustris, with the larger cell nearly three millimetres in length. The flecks of green inside it are endosymbiotic algae. Photo from here.

The Pelobiontida contain three distinct genera, Pelomyxa, Mastigina and Entamoeba, united by molecular data. Mastigina and Pelomyxa are both free-living amoeboflagellates. Mastigina setosa has one or a few nuclei and a single long cilium; however, movement is by pseudopodia while the cilium contributes little if any propulsion. Pelomyxa palustris is a gigantic amoeboid, up to five millimetres long and often with hundreds of nuclei in a single cell. It possesses small cilia, but it almost goes without saying that they do not contribute to moving the cell's massive bulk. Cytoplasmic movement in Pelomyxa has been described as "fountain streaming" - a wave of cytoplasm moves across the dorsal surface of the cell and spills over the front. Like Trichosphaerium, Pelomyxa can reproduce by budding off a piece of the cell with a few nuclei (Hickson, 1909) - indeed, at one point it was thought that Pelomyxa never underwent mitosis, an error that lead to its brief elevation to the status of an independent phylum, Caryoblastea.

Both of the two archamoebaen clades have given rise to non-ciliate lineages - the Endolimacidae (Endolimax and Endamoeba) among mastigamoebids, and Entamoeba among pelobionts. Both of these taxa are animal endosymbionts, living inside the gut of their host (the name Endolimax means "inner slug") - Endolimax and Entamoeba inhabit vertebrates (including humans), while Endamoeba is found in cockroaches (including termites). Endolimacidae are generally innocuous, but a few species of Entamoeba can cause great trouble for their hosts - among humans, E. histolytica causes dysentery, while E. gingivalis lives in the mouth and can cause gum disease.

Endamoeba blattae, an inhabitant of the digestive system of cockroaches. Photo from here.

Even with the downfall of the idea that Archamoebae are among the most archaic of eukaryotes (which kind of makes the name of clade a bit misleading, but we're stuck with it now), the relationships of this group are still interesting. Archamoebae possess a distinct conical arrangement of microtubules at the base of the cilium; in turn, this cone sits on top of the nucleus like a Vietnamese farmer's hat. The presence of a similar structure in many slime moulds lead Cavalier-Smith to unite Archamoebae and Mycetozoa in a clade called Conosa (or Conosea, depending on which paper you're reading and what rank Cavalier-Smith felt like putting it at at the time). Molecular data generally supports placing the two close together, but not always as an exclusive clade - often various examples of the taxa described in the last post muscle their way in. Many of these other amoebozoans, such as Phalansterium and Multicilia, possess similar (but not identical) microtubular cones, and Cavalier-Smith (2009) recently extended the Conosa to include these taxa as well. This extended Conosa is supported by most molecular analyses, but it has to be noted that all of the taxa involved show elevated rates of evolution - Pelomyxa and Trichosphaerium, in particular, show rates going through the roof - and the possibility of long-branch attraction cannot be entirely ruled out. If I may be allowed a somewhat strained analogy, it's a bit like when an election is held in a culturally diverse area between candidates of various backgrounds and both sexes, and all the winning candidates end up belonging to one particular subgroup. It's entirely possible that this was the valid result, and nothing untoward occurred in the ballot-counting process, but still, you can't help wondering.

And with that, I reach the end of the Amoebozoa (at least for now). If you want to look back on the other amoebozoan posts:

Putting the Formless in Formation

Breviata anathema

TAFKAMI

TAFKAMI Walks

The Paragons of Amoeboids

Amoeba: Much Wierder than You Think

Keeping a Low Profile

The Diversity of Slime Moulds

incertae sedis

Amoebozoan Oddments

Now if only someone would do the same for Heterolobosea...

REFERENCES

Cavalier-Smith, T. 2009. Megaphylogeny, cell body plans, adaptive zones: causes and timing of eukaryote basal radiations. Journal of Eukaryotic Microbiology 56 (1): 26-33.

Cavalier-Smith, T., E. E.-Y. Chao & B. Oates. 2004. Molecular phylogeny of Amoebozoa and the evolutionary significance of the unikont Phalansterium. European Journal of Protistology 40 (1): 21-48.

Gill, E. E., S. Diaz-Triviño, M. J. Barberà, J. D. Silberman, A. Stechmann, D. Gaston, I. Tamas & A. J. Roger. 2007. Novel mitochondrion-related organelles in the anaerobic amoeba Mastigamoeba balamuthi. Molecular Microbiology 66 (6): 1306–1320

Hickson, S. J. 1909. The Lobosa. In A Treatise on Zoology pt. 1. Introduction and Protozoa, first fascicle (R. Lankester, ed.) Adam & Charles Black: London.

Walker, G., A. G. B. Simpson, V. Edgcomb, M. L. Sogin & D. J. Patterson. 2001. Ultrastructural identities of Mastigamoeba punctachora, Mastigamoeba simplex and Mastigella commutans and assessment of hypotheses of relatedness of the pelobionts (Protista). European Journal of Protistology 37 (1): 25-49.

Amoebozoan Oddments

noreply@blogger.com (Christopher Taylor) — Tue, 15 Sep 2009 03:19:00 +0000

Arachnula, a branched marine amoeboid of uncertain affinities. Photo by D. Patterson et al.

If I am to continue with the Cavalier-Smith et al. (2004) classification of Amoebozoa, the next class I reach would be the Variosea. However, Cavalier-Smith et al.'s Variosea was the weakest of the classes they recognised. The characters it was based upon (usually single cilia or centrosomes, no fruiting bodies, non-eruptive pseudopodia) are almost certainly plesiomorphic for Amoebozoa (or possibly the clade of Amoebozoa excluding Breviata), and even the name 'Variosea' was coined to refer to the diverse morphologies the class covered. Molecular studies have not indicated variosean monophyly, though the majority of 'varioseans' may fall into a paraphyletic series below Archamoebae and Mycetozoa. The Smirnov et al. (2005) classification contained no grouping comparative to Variosea: they simply left the 'varioseans' as "Amoebozoa incertae sedis". Still, this is as good a place as any to introduce the 'varioseans', plus a couple of other amoebozoan taxa that don't fall under the aegis of any of the other groupings I've referred to. In no particular order, these are the 'Varipodida', Centramoebida (or Acanthopodida), Stereomyxa, Corallomyxa, Phalansterium, Trichosphaerium and Multicilia.

The name 'Varipodida' was introduced by Cavalier-Smith et al. (2004) for a grouping of the non-ciliate genera Gephyramoeba and Filamoeba (though as it turns out 'Gephyramoeba' was misidentified; the varipodidan has been redescribed as Acramoeba, while true Gephyramoeba is a member of Leptomyxida and hence tubulinean; Smirnov et al., 2008). Subsequent studies have been equivocal about the monophyly of such a grouping. Generally, the two genera are close to the clade containing Archamoebae and Mycetozoa (more on that clade in the next post), either just outside it or just within it. Filamoeba is a flattened, fan-shaped amoeboid which produces extremely slender, spine-like subpseudopodia that look superficially like filose pseudopodia (hence the name). However, unlike true filose pseudopodia as found in Rhizaria, the subpseudopodia of Filamoeba do not function in movement. Acramoeba has branched cells, with the branches producing slender subpseudopodia like those of Filamoeba. It's also worth mentioning Arachnula, which is similar to Acramoeba but larger and multinucleate. Similar slender subpseudopodia are also produced by dictyostelian slime moulds, adding further support to a relationship between Varipodida and Mycetozoa.

Balamuthia mandrillaris. Photo from here.

The Centramoebida include the flattened soil-living amoebae Acanthamoeba and Balamuthia. Acanthamoeba is similar to Filamoeba in producing slender subpseudopodia (there was a picture in this post), but Balamuthia does not. Both genera can be pathogenic to humans, though that is probably not their main mode of life - Acanthamoeba has been connected to eye infections, while both Acanthamoeba and Balamuthia can cause meningitis. The really interesting thing about the centramoebids, however, is that unlike any of the amoebozoans I've covered in the last few posts, they possess a centrosome. The centrosome is an organelle that is involved in controlling the activity of the microtubules that run through the cytoplasm. The centrosome (or, specifically, the centrioles within the centrosome) is also the organelle responsible for the production of cilia. Up until now, I've been looking at non-ciliate amoebozoans, but the common ancestor of the Amoebozoa would have been ciliate and some amoebozoans remain so. Just how many times cilia have been lost in the Amoebozoa is unknown - at least five, probably more (Nikolaev et al., 2006). Centramoebids have lost the cilium and the centrioles, but they still retain the evidence of their former presence in the centrosome.

Corallomyxa, though without a species name I'm not certain whether this is supposed to be true Corallomyxa or the rhizarian Filoreta tenera, originally misidentified as a Corallomyxa. Photo by David Patterson.

A similar centrosome to that of Centramoebida is also found in the marine genera Stereomyxa and Corallomyxa, and the three taxa may form a clade (Cavalier-Smith et al., 2004). Stereomyxa and Corallomyxa have slender branched, reticulate pseudopodia, making them look at first glance a bit like a small plasmodial slime mould (though they differ in lacking fruiting bodies). A recent study suggesting that Corallomyxa, at least, may be rhizarian rather than amoebozoan has turned out to be based on another misidentification (Bass et al., 2009).

Trichosphaerium in the naked phase. Photo by David Patterson.

Trichosphaerium is perhaps the most bizarre of all the amoebozoans - and not merely because of its ability to happily chow down on plastic. Trichosphaerium is a relatively large, multinucleate marine amoeboid that lives enclosed in a membranous test. The test is pierced by numerous openings, and the amoeboid extends its pseudopodia through those openings for feeding and locomotion (this differs from the situation in Pellita because the openings are permanent, rather than each individual pseudopodium forcing its way out through the covering). The life cycle of Trichosphaerium alternates between asexual and sexual generations; in the asexual generation, the test has a covering of sharp spicules, but in the sexual generation it is smooth. Reproduction in the asexual stage is by division, but division is generally unequal - a relatively small piece of cytoplasm containing a few nuclei is pinched off to become a separate cell, and the nuclear membrane does not break down during division. In the sexual generation, asexual division may occur as in the asexual generation while the cell is growing, but when the cell finishes growing it forms a cyst. Within the cyst, the cell divides rapidly so that each individual nucleus is contained within its own individual biciliate cell; when the cyst breaks open, these uninucleate cells fuse to give rise to the next generation (Hickson, 1909). Under crowded conditions, normal multinucleate cells have also been recorded fusing to give rise to gigantic amoeboid cells up to three millimetres in diameter, with over a thousand nuclei, that break apart into more normal multinucleate within the course of a week.

Phalansterium - drawing of a colony and of an individual cell embedded in its matrix. Image by Stuart Hedley & David Patterson.

Phalansterium is another highly unusual amoebozoan, for the simple reason that it is not an amoeboid (Cavalier-Smith et al., 2004). It's not even an amoeboflagellate. At one time, Phalansterium was united with the choanoflagellates, which it resembles in having a collar around the base of its single cilium and by living in colonies; however, in Phalansterium the collar is a single undivided fold while in choanoflagellates it is divided into microvilli, while Phalansterium has only a single centriole at the base of its cilium to choanoflagellates' two. Molecular analysis firmly plonks Phalansterium among the amoebozoans. Cavalier-Smith has made some pretty big calls in relation to unassuming little Phalansterium, claiming it is the closest known organism to the probable ancestral morphology for all eukaryotes. This, however, is based on his assumption that the unikont morphology is ancestral.

Drawing of Multicilia instructa. Image by Won Je Lee.

Finally, Multicilia is a marine amoebozoan with a covering of numerous radially-arranged cilia. Mikrjukov & Mylnikov (1998) found that movement in Multicilia was by irregular, uncoordinated beating of the flagella, causing the cell to roll over the substrate without any obvious organisation into front or back or up or down. Short pseudopodia are extended to capture Multicilia's favoured food - other amoebozoans. Generally cells are roughly globular, but in certain unfavourable conditions large branched cells can develop. Cavalier-Smith et al. (2004) suggested that Multicilia was related to the Flabellinea due to the presence of glycostyles in the cell coat, but Nikolaev et al. (2008) placed it closer to other ciliate amoebozoans.

REFERENCES

Bass, D., E. E.-Y. Chao, S. Nikolaev, A. Yabuki, K. Ishida, C. Berney, U. Pakzad, C. Wylezich & T. Cavalier-Smith. 2009. Phylogeny of novel naked filose and reticulose Cercozoa: Granofilosea cl. n. and Proteomyxidea revised. Protist 160 (1): 75-109.

Cavalier-Smith, T., E. E.-Y. Chao & B. Oates. 2004. Molecular phylogeny of Amoebozoa and the evolutionary significance of the unikont Phalansterium. European Journal of Protistology 40 (1): 21-48.

Hickson, S. J. 1909. The Lobosa. In A Treatise on Zoology pt. 1. Introduction and Protozoa, first fascicle (R. Lankester, ed.) Adam & Charles Black: London.

Mikrjukov, K. A., & A. P. Mylnikov 1998. The fine structure of a carnivorous multiflagellar protist, Multicilia marina Cienkowski, 1881 (Flagellata incertae sedis). European Journal of Protistology 34: 391-401.

Nikolaev, S. I., C. Berny, N. B. Petrov, A. P. Mylnikov, J. F. Fahrni & J. Pawlowski. 2006. Phylogenetic position of Multicilia marina and the evolution of Amoebozoa. International Journal of Systematic and Evolutionary Microbiology 56: 1449-1458.

Smirnov, A. V., E. S. Nassonova & T. Cavalier-Smith. 2008. Correct identification of species makes the amoebozoan rRNA tree congruent with morphology for the order Leptomyxida Page 1987; with description of Acramoeba dendroida n. g., n. sp., originally misidentified as ‘Gephyramoeba sp.’ European Journal of Protistology 44 (1): 35-44.

Smirnov, A. V., E. S. Nassonova, E. Chao & T. Cavalier-Smith. 2007. Phylogeny, evolution, and taxonomy of vannellid amoebae. Protist 158 (3): 295-324.

Building a Home of Your Own (Taxon of the Week: Hydroides)

noreply@blogger.com (Christopher Taylor) — Mon, 14 Sep 2009 03:40:00 +0000

Close-up of the front end of the tubeworm Hydroides elegans, showing the double-level operculum. Photo by John Lewis.

This week's highlight taxon is the worm genus Hydroides. Hydroides unites about eighty species of the family Serpulidae, the tubeworms, an easily-found component of many a beach all over the world. Serpulids (previously commented on here) are a distinctive group of annelid worms that secrete themselves a tubular shell of calcium carbonate in which they live permanently attached to a rock or some other substrate (not uncommonly, that "other substrate" will be another tubeworm, leading to the production of tangled masses of worm tubes). Many authors have divided serpulids between two families, Serpulidae proper and Spirorbidae, but phylogenetic studies place spirorbids as a derived subgroup of Serpulidae rather than their sister group (Kupriyanova et al., 2006; Lehrke et al., 2006). Hydroides is not a spirorbid, so it remains in Serpulidae whatever the preferred arrangement.

With more than eighty species, Hydroides is a reasonably large assemblage, and it is distributed worldwide. Among the more distinctive features of the genus is the division of the spinose operculum into two tiers, a lower (rather daisy-like, in my opinion) ring called the funnel and an upper ring of spines called the verticil. The features and arrangement of the verticil spines are often the main distinguishing characters between species, but this can be complicated somewhat by changes in spine morphology over the course of growth and regeneration (ten Hove & Ben-Eliahu, 2005). It is also notable that at least one Caribbean species, Hydroides spongicola, has been recorded as showing a tendency towards reduction of the operculum; this species lives in close association with the highly toxic touch-me-not sponge (Neofibularia nolitangere) and presumably the host sponge's irritating spicules offer all the protection the tubeworm needs (Lehrke et al., 2006).

The first species of Hydroides to be described was H. norvegica (now Hydroides norvegicus to match the gender of the genus) in 1768 by Johan Ernst Gunnerus, Bishop of Trondhjem*. An English translation of Gunnerus' original description was published by Moen (2006); as shown in the reproduction above from Moen (2006) of the first few lines, the original is not among the easiest of reads. Interestingly enough, Gunnerus bestowed a different name on the animal ("Hydroides norvegica") from the tube that it lived in ("Serpula norvegica") - I suspect that this may represent a different philosophy from the present about how to deal with animals versus their products, as opposed to any doubt about whether the one had produced the other. In a letter to Linnaeus (or von Linné as he'd become by then), Gunnerus also described his doubt about just what type of animal it was he'd described - a hydrozoan, or possibly a sea cucumber? It seems that its sessile lifestyle had quite put him off the idea of it being a worm**.

*Among other animals described by Gunnerus are the basking shark and Lineus longissimus, the world's longest ribbon worm and possibly the longest of all living animals.

**Remember, Gunnerus and Linnaeus were both working in a largely non-evolutionary paradigm. As such, their classifications were not intended to reflect an organism's "affinities" in the sense that we'd understand them, but rather to reflect how their overall features compared to other animals.

Congregation of Hydroides ezoensis on the side of a ship. Image from Science in Salamanca.

These days, Hydroides species are among the most intensely studied of all marine annelids. The motives for this interest are primarily economical - not surprisingly, Hydroides have often earned the ire of humans through their penchant for attaching themselves to the humans' nice clean boats and jetties. A number of Hydroides species have been transported and established outside their native ranges by human agency - probably in ballast water for the most part, though H. ezoensis was transported from Japan to France on the shells of oysters imported to stock oyster farms (Thorp et al., 1987). With this economic focus, it is not surprising that the majority of studies appear to have been on factors affecting larval development and settlement. One interesting point is that Hydroides larvae are far more likely to settle somewhere already inhabited by tubeworms than on a completely fresh surface (Scheltema et al., 1981), a common pattern among sessile organisms that do not reproduce by budding. After all, there's safety in numbers.

REFERENCES

Hove, H. A. ten, & M. N. Ben-Eliahu. 2005. On the identity of Hydroides priscus Pillai 1971 – taxonomic confusion due to ontogeny in some serpulid genera (Annelida: Polychaeta: Serpulidae). Senckenbergiana Biologica 85 (2): 127-145.

Kupriyanova, E. K., T. A. Macdonald & G. W. Rouse. 2006. Phylogenetic relationships within Serpulidae (Sabellida, Annelida) inferred from molecular and morphological data. Zoologica Scripta 35: 421-439.

Lehrke, J., H. A. ten Hove, T. A. Macdonald, T. Bartolomaeus & C. Bleidorn. 2006. Phylogenetic relationships of Serpulidae (Annelida: Polychaeta) based on 18S rDNA sequence data, and implications for opercular evolution. Organisms Diversity & Evolution 7 (3): 195-206.

Moen, T. L. 2006. A translation of Bishop Gunnerus’ description of the species Hydroides norvegicus with comments on his Serpula triqvetra. Scientia Marina 70S3: 112-123.

Scheltema, R. S., I. P. Williams, M. A. Shaw & C. Loudon. 1981. Gregarious settlement by the larvae of Hydroides dianthus (Polychaeta: Serpulidae). Marine Ecology Progress Series 5: 69-74.

Thorp, C. H., S. Pyne & S. A. West. 1987. Hydroides ezoensis Okuda, a fouling serpulid new to British coastal waters. Journal of Natural History 21 (4): 863-877.

Catalogue of Organisms

Thistle Be The One (Taxon of the Week: Carduoideae)

"Electronic Publication of Nomenclatural Acts is Inevitable"

Name That Bug: Ponopterix axelrodi

Name That Bug # 4

Name That Bug: Meioneurites spectabilis

Name That Bug # 3

Cranes Off the Rails (Taxon of the Week: Grues)

Name That Bug: Stoecharthrum giardi

Name That Bug # 2

Name That Bug: Cornu aspersum

Name That Bug #1

Time For Teeth (Taxon of the Week: Polygnathus)

Fungus and the Individual

Careful with that Spelling (Taxon of the Week: Barleeiidae)

Some Thoughts on How to Make Electronic Publication Work

Crabs That Cannot Scratch Their Heads (Taxon of the Week: Parthenopidae)

If They Only Wood (Taxon of the Week: Diaporthales)

Secret Identities

Taxonomy Trivia Quiz #2: You've Come a Long Way, Baby

&*^%$* Americans, Think They Own the Internet....

A South American Paradox (Taxon of the Week: Sellocharis)

The Voice of the Turtle (Taxon of the Week: Streptopelia)

Archamoebae: The Apogee (or Nadir) of Amoebozoan Evolution

Amoebozoan Oddments

Building a Home of Your Own (Taxon of the Week: Hydroides)

&^%$ Americans, Think They Own the Internet....