Carpospores in Chains (Taxon of the Week: Schizoserideae)

Drachiella spectabilis, one of the few species of Schizoserideae found in the North Atlantic. Note the characteristic iridescence of the fronds. If you look very closely at the photo, you can also see one other characteristic of the family Delesseriaceae to which this species belongs - the fronds are so thin that you can see the features of the rock the alga is growing on through them. Photo by Keith Hiscock.

Despite being the most speciose clade of multicellular marine algae, I must admit I find that the Macrorhodophytina* (multicellular red algae) are not that easy to get a handle on. Most of the significant distinguishing features of various groups of red algae are at the cellular level, and often wrapped up in the eye-wateringly complicated life cycles many macrorhodophytes indulge in. So before I wrote this post, I had to spend a certain amount of time looking up things like just what a "gonimoblast" is. I hope I got it right.

*If you're wondering why I didn't use the name Rhodophyta, that's because Rhodophyta is a larger clade that also includes a few unicellular forms.

The Schizoserideae are a tribe of the red algal family Delesseriaceae containing five genera - Schizoseris, Neuroglossum, Abroteia, Drachiella (Lin et al., 2002) and the recently described Nancythalia (Millar et al., 2002). Delesseriaceae is a large family of red algae with very thin fronds (sometimes only a single cell thick) that may be anything from flat, broad and unbranched to very feathery; however the fronds are not filamentous or polysiphonous (a tubular construstion with a central axial cell surrounded by pericentral cells), distinguishing Delesseriaceae from other families in the order Ceramiales. Ceramiales are in turn distinguished from other red algal orders by the mode of formation of the auxiliary cell. To explain what an auxiliary cell is, I have to tell you that Ceramiales, like many other red algae, alternate between not just two but three distinct generations. As well as having separate multicellular haploid and diploid generations (as also found in many other algae and plants), there is a third stage called the carposporophyte. Mature diploids produce haploid spores that settle and grow into mature male or female haploids. The male haploids release sperm that fertilise the females. However, the resulting zygotes are not released; instead, the diploid nucleus of the zygote abandons the zygote and invades a nearby cell to produce the auxiliary cell (in Ceramiales, the cell that becomes the auxiliary was previously one of the supporting cells for the female gamete). The auxiliary cell then gives rise to a small diploid that remains parasitic on the parent haploid - this is the carposporophyte. The carposporophyte produces diploid spores that grow into new independent diploids.


Mature carposporophyte of Schizoseris condensata, showing the large, branching central fusion cell. Figure from Hommersand & Fredericq (1997).

In members of the Schizoserideae, the female gametangium (the procarp) contains four cells called carpogonia, one of which will get fertilised by the sperm, as well as one or two basal and one or two lateral sterile cells. After the fertilised zygote nucleus has entered the auxiliary cell, the carpogonial cells fuse to form a (wait for it) fusion cell. The auxiliary cell then gives rise to the filaments of the carposporophyte (these are the gonimoblast filaments, in case you were still wondering what that was), which in turn produce the carpospores (diploid spores) in long chains. After forming the carpospore chains, the gonimoblast cells then also fuse with the fusion cell, which ends up being a large, candelabra-shaped supportive structure for the carpospore chains; this candelabra-shaped fusion cell is one of the distinguishing characters for the Schizoserideae* (Hommersand & Fredericq, 1997). Other distinguishing features include the lack of protective covering cells on the procarps, and the arrangement of cell nuclei within the fronds - in growing parts of the fronds, all the nuclei line up in a single plane. As well as the morphological characteristics, the tribe has also been supported by molecular analysis (Lin et al., 2001).

*And just to show how much I do for you - those four sentences were the result of probably about an hour of me reading and re-reading the original paper trying to work out just what the heck was going on.


Sections through fronds of Schizoseris condensata, showing the linear arrangement of nuclei. In the bottom section, the alignment is breaking apart in the older part of the frond to the right. Figures from Hommersand & Fredericq (1997).

The main centre of distribution for the Schizoserideae is in the Southern Hemisphere; Abroteia and Nancythalia are both (as far as is known) monotypic and endemic to New Zealand (Millar et al., 2002). The genus Drachiella is the exception, with three of its four species found in the northern Atlantic and the fourth species described only recently from Taiwan and the Philippines (Lin et al., 2002).

REFERENCES

Hommersand, M. H., & S. Fredericq. 1997. Characterization of Schizoseris condensata, Schizoserideae trib. nov. (Delesseriaceae, Rhodophyta). Journal of Phycology 33 (3): 475-490.

Lin, S.-M., S. Fredericq & M. H. Hommersand. 2001. Systematics of the Delesseriaceae (Ceramiales, Rhodophyta) based on large subunit rDNA and rbcL sequences, including the Phycodryoideae, subfam. nov. Journal of Phycology 37: 881-899.

Lin, S.-M., J. E. Lewis & S. Fredericq. 2002. Drachiella liaoii sp. nov., a new member of the Schizoserideae (Delesseriaceae, Rhodophyta) from Taiwan and the Philippines. European Journal of Phycology 37: 93-102.

Millar, A. J. K., & W. A. Nelson. 2002. Nancythalia humilis gen. et sp. nov. and Abroteia suborbiculare (Delesseriaceae, Rhodophyta) from New Zealand. Phycologia 41 (3): 245-253.

The Endosymbiotic Hammer Strikes Again

I was going to write a post here about Lake's (2009) proposal in yesterday's Nature that double-membraned (Gram-negative) bacteria could be derived from an endosymbiotic relationship between two single-membraned bacteria (see this earlier post for an explanation of double- versus single-membraned bacteria), and why I found it decidedly unconvincing. But I've spent today trying (unsuccessfully, I might add) to look at seminal receptacles in harvestman ovipositors and overexposure to the smell of clove oil has left me feeling decidedly crook and put my brain into shutdown. So I'll just give you the link and the abstract, and a few things to keep in mind when reading the article (if you can get access to it):

Lake, J. A. 2009. Evidence for an early prokaryotic endosymbiosis. Nature 460: 967-971.

Endosymbioses have dramatically altered eukaryotic life, but are thought to have negligibly affected prokaryotic evolution. Here, by analysing the flows of protein families, I present evidence that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium. The resulting taxon has been extraordinarily successful, and has profoundly altered the evolution of life by providing endosymbionts necessary for the emergence of eukaryotes and by generating Earth’s oxygen atmosphere. Their double-membrane architecture and the observed genome flows into them suggest a common evolutionary mechanism for their origin: an endosymbiosis between a clostridium and actinobacterium.

Point 1: If such an endosymbiosis had occurred, then both partners would have probably had cell walls (peptidoglycan layers) outside their membrane (the only single-membraned eubacteria lacking cell walls are Mollicutes, which are parasites of eukaryotes*). Why did the external partner lose its cell wall rather than the internal partner?

*I originally referred to Mollicutes as intracellular - thankfully, Elio Schaechter put me right (they're extracellular). I did say that my brain had stopped working.

Point 2: The endosymbiosis scenario requires that the genetic complement of the external partner be entirely lost or transferred to the inner partner (as well as the greater part of its cytoplasm). While unusual, this would not be unique. Transfer of genes from one partner to the other is a common (if not universal) event in endosymbioses. The hydrogenosomes found in some anaerobic eukaryotes are generally accepted to be derived from mitochondria, but most have entirely lost their genomes (as far as we know). Also, in most secondary or tertiary chloroplasts, the eukaryotic genome of the endosymbiont has disappeared. However:

Point 3: In all established cases of endosymbiosis, gene transfer or loss has been mostly (if not entirely) to the cost of the internal partner. This applies not just to mutualist endosymbionts, but also to intracellular parasites. Lake's proposed endosymbiosis requires the transfer to happen the other way, at the cost of the external partner (offhand, the same objection applies to scenarios that propose an endosymbiotic origin for the eukaryotic nucleus).

Point 4: Even if Lake's premise that double-membraned bacteria carry genes from two phylogenetically separate ancestors is correct (I have to confess that I don't feel knowledgeable enough to critique that point), that doesn't necessarily require an endosymbiosis. A simple symbiosis might possibly be sufficient. Many bacteria form closely-linked ectosymbiotic consortia, and the well-established propensity of bacteria to swap genetic material like trading cards could result in a substantial transfer in such an arrangement over time. Also:

Point 5: Among eukaryotes, the endosymbiosis theory receives something of a boost from the point that eukaryotes are absolutely lousy with endosymbionts at all stages of interdependence. Lake mentions the proteobacterium Buchnera in aphids; there are also zooxanthellae in corals and clams, Perkensiella in amoebae, a whole universe of intracellular parasites... the list goes on. Prokaryotes, in contrast, just don't seem to carry endosymbionts to the same degree. Lake mentions in his support that the aforementioned Buchnera carries its own endosymbiont; what he doesn't mention is that this is the only well-established case of an endosymbiont inside a prokaryote. Lake claims that the Chlorochromatium consortium is very close to an endosymbiotic relationship. It's still ectosymbiotic nonetheless. Contrast this with the extreme general diversity and versatility of prokaryotes, which is leagues ahead of that of eukaryotes - you'd think that if they could easily do it, they would be.

Point 6: The presence of a nucleus of sorts in Planctomycetaceae indicates that bacteria are not incapable of developing new membrane systems.

Point 7: I really, really hate this paragraph:

In fact, the membrane organization of double-membrane prokaryotes fundamentally differs from that found in single-membrane prokaryotes. In the former, the peptidoglycan layer is sandwiched between the outer and inner membranes, so that it surrounds the inner membrane: in contrast, in the latter there is no inner membrane, and the peptidoglycan layer, located outside the cell, surrounds the outer membrane. Also, double-membrane prokaryotes contain their flagellar motors in the inner membrane, whereas single-membrane prokaryotes contain their flagellar motors in the outer membrane. And the photosynthetic apparatus in double-membrane prokaryotes is in the inner membrane, rather than in the outer membranes as in single-membrane prokaryotes. In other words, the organization of the inner membrane of the double-membrane prokaryotes resembles that of the outer membranes of typical single-membrane prokaryotes. The inner membranes of double-membrane prokaryotes are organized almost as if they were derived from the outer membrane of an engulfed single-membrane prokaryote.

This, ladies and gentlemen, is a classic case of semantic silly buggers. Lake obfuscates the difference between single- and double-membrane bacteria by noting that double-membrane bacteria have an outer and inner membrane, then referring to the membrane in single-membrane bacteria as the outer membrane even though it is positionally comparable to the inner membrane (pause to wipe foam from frothing mouth and allow bulging eyeballs to return to their sockets). His referral to the supposed difference between flagella of the two types of bacteria looks a little different when you consider that what he is saying is that both anchor their flagella on the membrane inside the cell wall. (noooo! the family curse!)

Point 8:

There is currently much discussion of the prokaryotic ‘tree of life’, but there are few points of agreement regarding its topology, except that it is not a tree.

While the idea that a tree is not an appropriate expression of prokaryote evolution is increasingly popular, I think it's jumping the gun a little to present it as a consensus. Take a look at the number of trees in an average issue of the International Journal of Systematic and Evolutionary Microbiology, for a start (and yes, now I am just picking at minor details).

Point 9: And just on a final quibble, this line from the supplementary info:

I propose the name Domain Synergia (Gr. Synergia – joint work) for those prokaryotes that possess the Gram negative, double membrane organization, and are derived from large, statistically significant gene flows from both the Actinobacteria (as defined in Table S1) and the Clostridia (also as defined in Table S1).

Not only would I consider it fairly unacceptable to bury the publication of a new taxon name within the online-only supplementary info of a print-based article, but under Lake's proposed scenario this "new" taxon would be circumscriptionally equivalent to the already-available name of Didermata.

Strangers from Parts Unknown (Taxa of the Week: Juncus section Juncotypus, Juncus amabilis)

Flowerhead of Juncus conglomeratus. If you look closely, you can see the line where the true stem ends, and the elongate stem-like flower bract begins. Photo from Nature Notes from Argyll.

Rushes of the genus Juncus are a large cosmopolitan assemblage of superficially grass-like plants, most commonly found in damp or swampy soils. A number of distinct subgroups are recognisable within the genus, and my subject today is one of those subgroups, the section Juncotypus in the subgenus Agathryon. Most older references will refer to this group as the subgenus or section Genuini, but the precendence of Juncotypus was noted by Kirschner et al. (1999)*. Both names, however, can be translated to give a good idea of what defines this group - section Juncotypus is the "genuine" rushes. Species of this species lack true leaves entirely (the leaves have been reduced to small sheaths at the base of the stem), and instead have clumps of umbranching photosynthetic stalks rising from a basal woody rhizome. The flower clusters appear to born laterally some way down the stalk (Healy & Edgar, 1980; though admittedly, calling the tiny wind-pollinated reproductive organs of rushes "flowers" arguably stretches the term to its limits), but are in fact not - rather, the part of the "stalk" extending past the inflorescence is really the flower bract.

*A few notes for my more zoologically-oriented readers. While zoological nomenclature allows only one formal division between species and genus, the subgenus, botanical nomenclature allows (from highest rank to lowest) subgenus, section, subsection, series and subseries. And while zoological taxonomists tend to be a little chary when it comes to using subgenera, botanical taxonomists have a long history of using every one of those subsidiary ranks to full capacity (some botanists have managed to pluck even further levels out of the ether). Also, while zoological taxonomy interpolates subgeneric names into the full species names (e.g. Brachiosaurus (Giraffatitan) brancai), botanical taxonomy does not - Juncus amabilis is a member of the section Juncotypus, but that doesn't mean that it should be called "Juncus (Juncotypus) amabilis". Finally, while zoological taxonomy regards subgeneric names as distinct entities at the same level of homonymy as generic names (Giraffatitan is nomenclaturally distinct from Brachiosaurus, and because the name has been used for a subgenus, it cannot be used for another genus or subgenus), botanical taxonomy regards the subgeneric name as directly connected to the generic name, so the proper name for today's subject is "Juncus section Juncotypus", not just "Juncotypus". One side-effect of this is that using a name for a subgeneric taxon in one genus does not prevent its use in association with another genus, so (e.g.) Crassula section Glomeratae and Campanula series Glomeratae are not regarded as homonyms.

If you're feeling horribly lost about now, take comfort in my assuring you that, yes, botanical nomenclature really is as horribly complicated as it looks. Personally, I don't understand a word of it.

Species of section Juncotypus are found in temperate habitats over most of the world. Some species are found in tropical latitudes, such as Juncus aemulans in Central America (Mexico to Guatemala) and Juncus decipiens in eastern Asia and New Guines, but at high altitudes (Snogerup et al., 2002; Wilson & Johnson, 2001). More than half the recognised species are found in Australasia, while a few species such as Juncus effusus are found over almost the entire range of the subgenus as either natives or adventives. Some members of the section are notable pasture pests. Though morphologically distinct, recent phylogenetic analyses have not supported the monophyly of the section Juncotypus (Drábková et al., 2006; Drábková & Vlček, 2009). Drábková & Kirschner (2004) particularly commented on the intermediate morphology of Juncus uruguensis between sections Juncotypus and Steirochloa. These results have not yet been incorporated into a taxonomic revision, probably because as yet only a relatively small number of Juncotypus species have been studied in this regard.


Juncus effusus. Photo from here..

Not surprisingly in light of their simple morphology, species of section Juncotypus have mostly been difficult to distinguish. In this regard, I can't do much better than steal wholesale the words of Edgar (1964):

Although the Junci Genuini show obvious differences of habit and colour in the field, these differentiating characters are largely lost in pressing and drying, and herbarium specimens are often difficult to determine. The principal characters which have been used to distinguish the plants are the general size, the presence or absence of lacunae in the pith of the stem, the varying compactness of the inflorescence, the number of stamens, and the relative size of the capsules. Yet none of these characters is wholly satisfactory. For instance, if the general size of the plant is used as a diagnostic character there is an obvious difficulty in placing intermediate sizes. Then, the appearance of the pith in longitudinal section, i.e., whether continuous or interrupted by air spaces, is a very useful feature, but is not constant within some of the species nor, on occasion, even within one plant. Only three species in New Zealand invariably have six stamens and all the others have normally three, though four, five, or even six stamens may be found in occasional flowers. Again, the structure of the inflorescence is constant in some species but extremely variable in others, the flowers are small and inconspicuous and the tepals lose most of their character on drying. Lastly, the ratio between capsule-length and tepal-length which can be a very useful diagnostic character in other groups of Juncus is more difficult to use in this subgenus. In the species with larger capsules it is quite reliable, but in the species with the smallest flowers the difference in length between capsule and tepals is rarely greater than 0.5 mm and usually very much less, so that the ratio between the lengths does not make a convenient diagnostic character.

Diagnostic features of Juncus amabilis. Images from here.

When she made this complaint, Edgar (1964) was reviewing the New Zealand species of "Juncus genuini". In that paper, she described a new species Juncus amabilis, which was distinguished by its small size, extremely dark red-purple basal sheaths and pointed capsules that were distinctly longer than the tepals. Juncus amabilis has a distinctly scattered distribution in New Zealand, with specimens recorded from Auckland, Waikato, the Bay of Plenty, southern Canterbury and Otago (for those unfamiliar with New Zealand geography, that leaves a big gap across the southern North Island and northern South Island without records).

It wasn't until later that the reason for this unusual distribution pattern became clear, when Juncus amabilis was also identified in damp wastelands (primarily along river edges) in southern Australia. It now appears likely that, in spite of where it was initially discovered, J. amabilis is not a native of New Zealand, but an introduction from Australia*. Within Australia, the distribution of J. amabilis remains scattered (a map can be seen here) but, while uncommon, the species does not seem to be regarded as particularly endangered. It looks as if habitat availability rather than human impact may be the cause of its rarity.

*This is unusual, but not unique. A number of organisms have been described as introductions before being recorded from their native ranges. Among harvestmen, for instance, the species Ibantila cubana was originally described (as the species name indicates) from Cuba. However, I. cubana is the only species of the Old World family Podoctidae recorded from the Americas and was collected in a botanical garden, so it is almost certainly an exotic (Kury, 2003). The original homeland of this species remains as yet unknown.

REFERENCES

Drábková, L., J. Kirschner & Č. Vlček. 2006. Phylogenetic relationships within Luzula DC. and Juncus L. (Juncaceae): a comparison of phylogenetic signals of trnL-trnF intergenic spacer, trnL intron and rbcL plastome sequence data. Cladistics 22 (2): 132-143.

Drábková, L., & J. Kirschner. 2004. Juncus uruguensis - a member of the section Juncotypus (Juncaceae, Juncus subg. Agathryon). Nordic Journal of Botany 22: 687-691.

Drábková, L. Z., & Č. Vlček. 2009. DNA variation within Juncaceae: comparison of impact of organelle regions on phylogeny. Plant Systematics and Evolution 278: 169-186.

Edgar, E. 1964. The leafless species of Juncus in New Zealand. New Zealand Journal of Botany 2: 177-204.

Healy, A. J., & E. Edgar. 1980. Flora of New Zealand vol. III. Adventive cyperaceous, petalous and spathaceous monocotyledons. P. D. Hasselberg, Government Printer: Wellington (New Zealand).

Kirschner, J., L. J. Novara, V. S. Novikov, S. Snogerup & Z. Kaplan. 1999. Supraspecific division of the genus Juncus (Juncaceae). Folia Geobotanica 34 (3): 377-390.

Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachnida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1-337.

Snogerup, S., P. F. Zika & J. Kirschner. 2002. Taxonomic and nomenclatural notes on Juncus. Preslia 74: 247-266.

Wilson, K. L., & L. A. S. Johnson. 2001. The genus Juncus (Juncaceae) in Malesia and allied septate-leaved species in adjoining regions. Telopea 9 (2): 357-397.

Score One for Biogeography

Gagrella cauricrepa, the new gagrelline from northern Queensland. Specimen photographed by yours truly (offhand, I think that in over two years, this may be the first time that I've used one of my own images on this site. Now you know why).

One morning as I was sitting down to morning tea shortly after I first arrived in Perth, I made the comment that it was very strange that no Gagrellinae had been recorded from Australia*. Species of the subfamily have been described from both New Guinea and the Solomon Islands, so one would expect to find them here as well - New Guinea and Australia were connected in very recent history, so in biogeographic terms the Torres Strait generally has not functioned as a barrier. Most organisms that are found on one side are also on the other. Why not gagrellines? Yesterday, I had a paper (alluded to in the earlier post) published that solves the mystery by establishing that there is no mystery at all. Gagrella cauricrepa Taylor, 2009 is the first species of Gagrellinae described from Australia. Maybe (more on that later).

*I hasten to note that I was at the museum at the time. I'm not normally in the habit of bringing up random enigmas of arthropodological biogeography in mixed company.

Gagrella cauricrepa is found in the Iron Ranges, which are located right near the northern end of the Cape York Peninsula (the pointy bit at the top end of Queensland). The location in the Iron Ranges also offers a neat explanation as to why Australian gagrellines are not more widespread - it is one of the few patches of true wet rainforest in Australia (most of the remaining forest on Cape York Peninsula is drier), so it is probably the shortage of suitable habitat that holds back the gagrelline advance. Torres Strait itself was no barrier at all*.

*Offhand, despite the universal recognition of the biogeographic identity between northern Queensland and southern Papua New Guinea, I found it surprisingly difficult to find supporting references for it. Few people bother to document what they think everybody knows.

Readers of my earlier post may raise an eyebrow at my placing the new species in the genus Gagrella. All I can say in my defense is that while I know that doing so was a completely stupid, senseless thing to do, all my other options were even more stupid and senseless. The paper does include a discussion of how stupid and senseless I was being.

One thing that you may not realise when reading the paper, on the other hand, is just how close I came to potentially making a prat of myself when writing it (you know, I could have quite easily kept my silence on this subject, but instead I will cheerfully dance for your amusement). My description of the first recorded Australian gagrelline had been submitted, reviewed, revised and was ready to print. Until, only a few days after submitting the final revisions, I was pulling stuff out of Roewer (1910) for the still-in-prep-and-probably-will-be-for-some-time-yet nomenclator, when I saw that Roewer's (1910) description of the new species Zaleptus marmoratus gave the locality as "Australien?" I had been scooped by some ninety-nine years! That was the reason behind the post on Maison Verreaux, who were the source of the Zaleptus marmoratus type specimen. I had not noticed any other gagrellines from Australia in any of the collections I went through, and as it turned out the reputation of Maison Verreaux for supplying specimens with sloppy if not entirely fabricated locality data means that the origin of Zaleptus marmoratus cannot be accepted unquestioningly. No other species of Zaleptus has been recorded east of Sumatra - even if Roewer's Zaleptus is not a monophyletic group (which is probably quite likely), I think the absence from the area of species of a 'zaleptean' morphology still counts for something in this case.

As explained in the paper, I also wasn't able to find any indication that Jules Verreaux (the only member of Maison Verreaux to visit Australia) had been far enough north in Queensland to be collecting gagrellines. This conclusion is somewhat more shaky - Jules himself never wrote an account of where he had been (I'm guessing that he probably didn't want to leave a paper trail), so I was dependent on other people's records ("Australia" was about as specific as a Verreaux label got). But in concert with the point that Jules' brother Édouard definitely was in south-east Asia in the early 1830s*, near where 'Zaleptus' species have been reliably recorded, I suspect that an Asian rather than Australian origin for Z. marmoratus is at least possible, if not really demonstrable in the absence of specimens other than the holotype. So while Gagrella cauricrepa may not be the first record of Gagrellinae from Australia, it is the first reliable record from Australia.

*Contrary to what I said in the paper, it seems likely that Édouard travelled in south-east Asia more than Jules. My potted summary of their movements relevant to Z. marmoratus (written rather hastily, so as not to lose the deadline) was drawn heavily from Jules Verreaux's obituary in The Ibis. Unfortunately (but perhaps fittingly), the Ibis obituary seems to have been misleading about a number of things. In particular, it states that:

In 1832 Jules Verreaux again summoned his brother to join him [in South Africa], and till 1837 they travelled together, making expeditions to the Philippine Islands and Cochin-China. In 1838, having amassed large collections, the brothers shipped their treasures on board the trading-vessel ‘Lucullus’, they themselves embarking in another ship bound for France. Most unfortunately the ‘Lucullus’ was totally lost; and the labours of several years, uninsured, perished with her.

In my paper, I interpreted this to mean that both brothers arrived in Asia in 1832, remained there until 1837, but lost all their Asian material when the 'Lucullus' sank (which would be something of a problem for an Asian origin of Z. marmoratus). However, going by other references (see the Maison Verreaux post, which was written later than the Gagrella cauricrepa paper), it seems more likely that one, the other, or both brothers together made a number of trips between Asia, Paris and/or South Africa between 1832 and 1837, and that when Jules Verreaux was returning to Paris with material shipped on the 'Lucullus', he was returning from South Africa, not Asia (frustratingly, I haven't been able to find anything that says exactly where the 'Lucullus' had left from). It says something about the difficulty of tracing a person when you can't even be certain what continent they were on.

REFERENCES

Taylor, C. K. 2009. Revision of the Australian Gagrellinae (Arachnida: Opiliones: Sclerosomatidae), with a description of a new species. Australian Journal of Entomology 48: 217-222.

The Perils of Peer Review

There is an awful lot of crap taxonomy out there. Incoherent ramblings, near-unidentifiable taxa, or "new" taxa of dubious distinction from their previously-published relatives are all too common. Because inadequate taxonomic works can create an enormous hurdle for subsequent workers*, many suggestions have been made on how to reduce the number of such publications. One point that I've heard raised a number of times recently is that the current ICZN places very few limits on where a new taxon can be published, and the suggestion has been made (at least informally) that only names published in peer-reviewed publications should be acceptable. While I can see the appeal in this proposal, I disagree - I don't think the ICZN should introduce such a requirement.

*As Charles Michener (1963) put it: "In other sciences the work of incompetents is merely ignored; in taxonomy, because of priority, it is preserved, and too much of the time of subsequent taxonomists is devoted to straightening out work of such people".

At the risk of stating the obvious, peer review is not a guarantee of quality. A lot of absolute dreck has survived the peer review process unscathed; a lot of excellent non-peer reviewed work has been published. Indeed, it is worth keeping in mind that formal peer review is, for the most part, a quite modern phenomenon. Until fairly recently, it simply wouldn't have been logistically feasible to send copies of a manuscript to multiple reviewers - especially for researchers in places like Australasia who were often working in isolation and for whom the only suitable reviewers would have been on the other side of the globe. A significant number of major taxonomic monographs that are still being referred to today were never peer reviewed.

There are also limitations to peer review that are particularly applicable to taxonomy. A reviewer of a manuscript is always forced to exercise a certain degree of faith in the author(s) he/she is reviewing. They can re-run the data analyses reported in the manuscript to see if the sums add up, they can try and think of any other analyses that the author(s) should have done but didn't, but generally they must first make the assumption that the author(s) are reporting their data accurately (almost the only alternative would be to re-run the entire investigation from scratch, an investment of time that most reviewers would simply not have the freedom to make). Unless there are great glaring holes in the reported data, most reviewers may not be likely to spot cases of fabrication, omission or basic error*. This is a particular limitation in taxonomy because of its often interpretive and material-dependent nature. If you present me with a manuscript saying "Specimen group A and specimen group B have the following distinct characters, and should be regarded as separate species", then I am limited in how much I can check this assertion because most likely I do not have access to your specimens.

*To give a practical example of what I'm trying to say: imagine you said to me, "Today I saw two red cars and one blue car; therefore, red cars are more common than blue cars". I can criticise your conclusion on the basis of the data you've given me (for a start, I would hardly think that three observations is a large enough sample to be statistically significant), but I would have no way of knowing whether you actually had seen two red cars and one blue car.

Of course, while both these points are worth keeping in mind, neither one is in itself a reason not to introduce a peer review requirement into taxonomy. The recency of peer review would not be likely to be a problem because most revisions of the Code have not been retroactive. And while peer review may not ensure that only quality work is published, it usually still acts as a general filter to prevent the worst abominations. The real reason why I don't think that the Code should introduce a peer review requirement is that if you are going to require something, you must first be clear about what it is that you are requiring.

Last year one of the big news items for vertebrate palaeontology was Aetogate, in which allegations of academic misconduct were levelled against an American palaeontologist and his associates. Without wanting to comment specifically on that whole sordid affair, one of the major take-home messages that I thought came out of it was the difficulty of defining "peer review". Among the accusations being made was that the journal publishing many of the allegedly offending articles could not really claim to be "peer reviewed", because the "reviewers" were made up of people closely connected to the journal itself and so not impartial. If the reviewers of a manuscript have a vested interest in the progress of that manuscript, then obviously their suitability as reviewers is questionable.

Unfortunately, the solution to this problem is not as simple as requiring that a manuscript must be reviewed by someone other than the author's nearest and dearest. If one is working in a specialist field that encompasses only a small number of workers, then there simply may not be any qualified reviewers other than one's nearest and dearest (or furthest and most loathed, which is arguably just as bad). And because the details of the review process are not usually made public (for perfectly valid reasons) there is usually no direct way of telling after publication what level of review a manuscript has passed through. As I've discussed in a previous post, it can often be contentious enough establishing whether or not a name has been properly published. Imagine the confusion that could ensue if subsequent workers had to establish whether it had been properly reviewed.

So what is the appropriate solution to inadequate taxonomy? As it happens, the ICZN already has some powerful tools up its sleeve. It has the ability to eliminate problematic names or, if necessary, entire publications from nomenclature. It is also worth noting that many of the workers who have suggested a peer review requirement are not considering just the simple quality of taxonomic work, but more its currently dispersed nature. In that case, a central registration system (currently being proposed and developed for the ICZN) may remove a large number of the current issues. Registration is a concept that is not without its issues, but at least determining whether or not a name has been registered would be much more straightforward than determining whether or not a name has been reviewed.

REFERENCES

Michener, C. D. 1963. Some future developments in taxonomy. Systematic Zoology 12 (4): 151-172.

How the Badger Became (Taxon of the Week: Meles thorali)

Reconstruction of Meles thorali from Lyras & van der Geer (2007).

Badgers of the genus Meles are found throughout temperate Eurasia. They are burrowing omnivores, primarily feeding on worms, insects and other invertebrates but also quite willing to take plant matter and small vertebrates (the proportion of the diet made up by each varies from place to place). Badger lifestyles are also varied - badgers in England may live in groups of up to thirty individuals, but in other parts of their range they are much more reclusive. Many authors recognise only a single modern species in the genus, Meles meles, but based on characters of the dentition, coloration and baculum morphology some authors have argued for the recognition of three species - M. meles in Europe and Russia west of the Volga river, M. leucurus in Asia east of the Volga (with M. meles and M. leucurus marginally overlapping in central Asia east of the Caspian), and M. anakuma (the smallest species) in Japan (Abramov & Puzachenko, 2005). However, both the two continental species include a number of subspecies, while genetic divergence overall is low, so this is an area that requires further investigation (Marmi et al., 2005).

The genus Meles probably divided from the ancestors of its current living sister taxon, the hog badger Arctonyx collaris of south-east Asia, some time around the beginning of the Pliocene* (Tedford & Harington, 2003). Meles gennevauxi from Montpellier in France is known from the Lower Pliocene, but opinions differ as to whether this should be included in Meles or Arctomeles (a fossil genus related to Arctonyx; Tedford & Harington, 2003; Arribas & Garrido, 2007). If M. gennevauxi loses its spot, the runner-up is the late Pliocene Meles thorali.

*Offhand, Meles and Arctonyx are now the only living members of the mustelid subfamily Melinae, which used to contain all the "badgers" except the honey badger Mellivora capensis. Recent studies have shown that "badgers" are a polyphyletic group, and they have been divided up accordingly (Koepfli et al., 2008). The south-east Asian stink badgers of the genus Mydaus are related to the American skunks (which have been excluded from the Mustelidae as a separate family, Mephitidae), the American badger Taxidea taxus is sister to all other mustelids, while the ferret badgers (Melogale) are closer to Mustela and otters.


Upper jaw of Meles thorali spelaeus, seen from below. Photo from the Museo de Prehistòria de València.

Meles thorali was described from Saint-Vallier in France by Viret (1950; I haven't seen the original description), and has since been recorded from Bulgaria and Lesbos (Lyras & van der Geer, 2007). A subspecies, Meles thorali spelaeus, has been described from the south of France (Bonifay, 1971), but again I haven't seen the original description. Meles thorali was similar in size to modern Meles meles, but was distinguished by features such as the lesser lateral projection of the zygomatic arches (the cheekbones) and the presence of only two instead of three or more roots on the lower second molar (Arribas & Garrido, 2007).

Other badger species present in Europe during the latest Pliocene and early Pleistocene were the Spanish M. iberica, M. dimitrius of Greece and M. hollitzeri of Germany. On purely phenetic grounds, M. iberica appears to be the most divergent of the European badgers, while M. dimitrius and M. hollitzeri were closer to M. thorali and M. meles. Genetic studies confirm the identity of modern Iberian badgers with M. meles (Marmi et al., 2005), and nearly one and a half millions years (not to mention a couple of ice ages) separate M. iberica from the earliest known Iberian M. meles (Arribas & Garrido, 2007). M. thorali has been suggested to be the ancestor to the modern Meles species (Baryshnikov et al., 2003), but it is notable that M. thorali spelaeus seems to be even closer morphologically to M. meles than M. thorali thorali - a fused root on the upper second premolar and a second lower molar wider than long are derived features of the first two not shared with the third (Arribas & Garrido, 2007). Moreover, if one considers M. thorali proper and not M. spelaeus, I don't see from the characters described by Arribas & Garrido (2007) why M. thorali is necessarily any closer to modern badgers than M. dimitrius or (particularly) M. hollitzeri - M. hollitzeri, for instance, is closer to modern badgers in molar morphology. While Baryshnikov et al. (2003) derive modern east Asian badgers as well as M. meles proper from M. thorali*, I don't know whether they considered the relatively little-mentioned early Pleistocene Chinese badgers M. chiai and M. teilhardi (Xue et al., 2006).

*That is, if I've understood the abstract correctly. Funnily enough, the Russian Journal of Theriology doesn't seem to be readily available here in Perth.

REFERENCES

Abramov, A. V., & A. Yu. Puzachenko. 2005. Sexual dimorphism of craniological characters in Eurasian badgers, Meles spp. (Carnivora, Mustelidae). Zoologischer Anzeiger 244 (1): 11-29.

Arribas, A., & G. Garrido. 2007. Meles iberica n. sp., a new Eurasian badger (Mammalia, Carnivora, Mustelidae) from Fonelas P-1 (Plio-Pleistocene boundary, Guadix Basin, Granada, Spain). Comptes Rendus Palevol 6: 545-555.

Baryshnikov, G. F., A. Yu. Puzachenko & A. V. Abramov. 2003. New analysis of variability of cheek teeth in badgers (Carnivora, Mustelidae, Meles). Russian J. Theriol. 1 (2): 133–149.

Bonifay, M. F. 1971. Carnivores quaternaires du Sud-Est de la France. Mem. Mus. natl Hist. nat., Paris, n.s., Ser. C 21 (2): 1–377.

Koepfli, K.-P., K. A. Deere, G. J. Slater, C. Begg, K. Begg, L. Grassman, M. Lucherini, G. Veron & R. K. Wayne. 2008. Multigene phylogeny of the Mustelidae: resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation. BMC Biology 6: 10.

Lyras, G. A., & A. A. E. van der Geer. 2007. The Late Pliocene vertebrate fauna of Vatera (Lesvos Island, Greece). Cranium 24 (2): 11-24.

Marmi, J., A. V. Abramov, P. V. Chashchin, & X. Domingo-Roura. 2005. Filogenia, subespeciación y estructura genética del tejón (Meles meles) en la Península Ibérica y en el mundo. In Ecología y conservación del tejón en ecosistemas mediterráneos (E. Virgós, E. Revilla, J. G. Mangas & X. Domingo-Roura, eds) pp. 13-26. Sociedad Española para la Conservación y Estudio de los Mamíferos: Málaga (reproduced as part of Josep Marmi's thesis).

Tedford, R. H., & C. R. Harington. 2003. An Arctic mammal fauna from the Early Pliocene of North America. Nature 425: 388-390.

Viret, J. 1950. Meles thorali n. sp. du loess villafranchien de Saint-Vallier (Drôme). Eclogae Geologicae Helvetiae 43 (3): 274–287.

Xue X., Zhang Y. & Yue L. 2006. Paleoenvironments indicated by the fossil mammalian assemblages from red clay-loess sequence in the Chinese Loess Plateau since 8.0 Ma B.P. Science in China: Series D Earth Sciences 49 (5): 518—530.

"Creodonts": Carnivores by Association

"Karianne's Pet" by Carl Buell. The large animal in the painting is the hyaenodontid Megistotherium osteothlastes, a contender for the title of biggest terrestrial carnivorous mammal ever.

As explained in an earlier post (which you may be interested in reading as a bit of background to this one), the earlier part of the Caenozoic (the current era of the earth's history) was home to a number of mammalian lineages of very mysterious relationships. Very few of the familiar orders around us today had yet put in an appearance, and instead the world was home to such oddities as pantodonts, tillodonts and dinocerates. Among the prominent carnivorous mammals of the time were a group known as the creodonts. Creodonts ranged in size from that of a small cat to lion- or bear-size species, and often converged in appearance with those animals. But what were creodonts?

Current authors regard the Creodonta as including two families, the vaguely cat-like Oxyaenidae and the largely dog- or hyaena-like Hyaenodontidae. Oxyaenids were found in North America and Europe during the late Palaeocene and Eocene, while hyaenodontids were found in Africa, Eurasia and North America from the Late Palaeocene to near the end of the Miocene, though they disappeared from North America not long after the end of the Eocene (Gheerbrant et al., 2006). Many authors have suggested a relationship with modern carnivorans (cats, dogs, weasels, bears, etc.), and they have been included with the latter in a superorder Ferae. Popular as this arrangement has been, however, there's just one small problem - there's not a shred of evidence to support it.


The oxyaenid Patriofelis ferox, reconstructed by Dmitry Bogdanov.

Part of the problem is that creodonts are a good example of what might be called "taxonomic drift". Imagine that an author establishes a taxon, and presents a list of organisms that he thinks belong to that taxon. A few years pass by, and the taxon is revised by another author, who excludes some of the originally-included species that he thinks belong elsewhere, and substitutes a few more species that he believes to be related to the remainder. Carry this on through a few subsequent revisions, with species being taken out and put in, and you may end up with a situation where nearly all of the original members of the taxon have been taken out, and the taxon name has become associated with a very different concept from its original intent. This can be horrendously confusing for later readers, because if they don't realise that this taxonomic drift has taken place, they may read things into older publications that their authors never intended.

Creodonta was originally established by Edward Drinker Cope in 1875 as a suborder of the Insectivora*. In his new suborder, Cope included three families - Oxyaenidae, Ambloctonidae (now included in Oxyaenidae - Gunnell, 1998) and Arctocyonidae (another contemporary family of carnivorous placentals, within which Cope also included what are now regarded as the Miacidae). The Hyaenodontidae were not part of the original Creodonta - at the time, Hyaenodon was regarded as a genuine carnivoran. Cope distinguished creodonts from carnivorans by the former's lack of a fused scapholunar bone in the wrist, their ungrooved astragalus, and their less-developed and smoother cerebral hemispheres (Cope, 1884). These features, it should be noted, are all primitive for placentals, but to Cope indicated the creodonts' position in the insectivoran grade. He nevertheless regarded creodonts as ancestral to carnivorans, with cats descended from Oxyaenidae and dogs from Miacidae (Cope, 1880). Later, Cope (1883) included Insectivora and Creodonta as separate suborders of his order Bunotheria, which also included the tillodonts, taeniodonts and prosimians**. Cope (1883) also redefined creodonts to include mammals without continuously-growing incisors and with trituberculate molars, which meant that in addition to the Oxyaenidae and Miacidae, Creodonta now included Mesonychidae, Leptictidae, moles and tenrecs (Arctocyonidae were transferred to the Insectivora). The Hyaenodontidae wormed their way in a year later (Cope, 1884).

*This does not necessarily mean that he thought they were specifically related to modern insectivorans such as shrews and hedgehogs. Cope and most of his contemporaries would have regarded the "Insectivora" as representing the generalised basal form from which all other placental mammals were derived, and recent insectivorans would have been the remnants of that original grade.

**It is also notable that Cope regarded the aye-aye as forming a separate suborder from other prosimians, due to its rodent-like incisors. Cope (1884) held that the tillodonts were "intimately allied to the living Chiromys [aye-aye] of Madagascar, which is itself almost a lemur, by general consent" (emphasis mine).


Skull of the sabre-toothed creodont Machaeroides eothen. Gunnell (1998) places Machaeroides in Oxyaenidae. Photo by Ghedoghedo.

So right from the beginning, the question of what was a creodont was convoluted. Over the years, various families of "creodonts" were reassigned as their relationships became clearer. The Miacidae became regarded as true Carnivora. Arctocyonidae and Mesonychidae became included among the primitive ungulates (another confused mess, but that's a story for another year) and may be related to artiodactyls. Moles and tenrecs, of course, were reunited with their fellow modern insectivorans (though the tenrecs have recently had another falling-out). Eventually, the creodonts were whittled down to their modern content of oxyaenids and hyaenodontids, but, as pointed out by Polly (1996), "Hyaenodontidae and Oxyaenidae are currently grouped together in Creodonta because they are the only taxa that have not been removed from the group, not because there has been specific positive evidence proposed for their grouping". Those few characters the two families do share are also found in other, non-creodont mammals. As for their association with Carnivora, the two orders have been associated because they both possess shearing carnassial teeth. However, while the carnassials in Carnivora are formed by the last upper premolars and the first lower molars, those of Oxyaenidae are derived from the first upper and second lower molars, while hyaenodontids have two sets of carnassials formed by the first upper/second lower and second upper/third lower molars. Carnassials have also developed in other groups of mammals - notably the borhyaenoids, which are metatherians if not marsupials and so definitely not related to carnivorans. The only real reason creodonts have been associated with Carnivora for so long seems to be their prior inclusion of the genuinely carnivoran (or stem-carnivoran) miacids. It's a bit like when one of your friends brings an acquaintance of theirs to a party who just hangs around for hours with everybody being too polite to ask them to leave.

So, if they weren't related to Carnivora, can we say what creodonts were related to? Particularly in the case of Oxyaenidae, the answer is brief, simple and to the point: we really have not got a sodding clue. Whatever their ancestry might have been, oxyaenids were horribly derived little (or not so little) beggars - for instance, they had completely lost the third molars. Van Valen (1969) derived both oxyaenids and hyaenodontids from the Palaeoryctidae, particularly from the Cretaceous-Palaeocene Cimolestes, and other authors seem to have regarded the idea favourably, at least for the hyaenodontids (Polly, 1996; Gheerbrant et al., 2006). The main problem with this scenario, however, is that the Palaeoryctidae of Van Valen and other authors is itself polyphyletic. For instance, the phylogenetic analysis of Wible et al. (2007) included two "palaeoryctids", Cimolestes and Eoryctes (Eoryctes is more likely to represent the Palaeoryctidae proper),and while Cimolestes appeared outside the placental crown group, Eoryctes was placed among the insectivorans as the sister to Potamogale (Tenrecidae). If creodonts (either or both families) are closer to Cimolestes, they may be stem-eutherians. If they are closer to Palaeoryctidae proper, they may even be afrotheres (Wible et al. did not support placement of tenrecs among afrotheres, but it is notable that the earliest hyaenodontids are African). Placement of either the Oxyaenidae or the Hyaenodontidae still awaits proper analysis.

REFERENCES

Cope, E. D. 1880. On the genera of the Creodonta. Proceedings of the American Philosophical Society 19 (107): 76-82.

Cope, E. D. 1883. On the mutual relations of the bunotherian Mammalia. Proceedings of the Academy of Natural Sciences of Philadelphia 35: 77-83.

Cope, E. D. 1884. The Creodonta. American Naturalist 18 (3): 255-267.

Gheerbrant, E., M. Iarochene, M. Amaghzaz & B. Bouya. 2006. Early African hyaenodontid mammals and their bearing on the origin of the Creodonta. Geological Magazine 143 (4): 475-489.

Gunnell, G. F. 1998. Creodonta. In Evolution of Tertiary Mammals of North America vol. 1. Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals (C. M. Janis, K. M. Scott & L. L. Jacobs, eds) pp. 91-109. Cambridge University Press.

Polly, P. D. 1996. The skeleton of Gazinocyon vulpeculus gen. et comb. nov. and the cladistic relationships of Hyaenodontidae (Eutheria, Mammalia). Journal of Vertebrate Paleontology 16 (2): 303-319.

Van Valen, L. 1969. The multiple origins of the placental carnivores. Evolution 23 (1): 118-130.

Wible, J. R., G. W. Rougier, M. J. Novacek & R. J. Asher. 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary. Nature 447: 1003-1006.

Wild Slug Chases (Taxon of the Week: Gastrodontoidea)

Daudebardia rufa (Oxychilidae) - note the small shell compared to the body. This species belongs to a subfamily, Daudebardiinae, that also happens to be carnivorous. Photo by Jiří Novák.

Before I get on to the subject of today's post - a bit of a gripe, and a bit of unsupported and unjustified speculation. I have a feeling that I'm not going to say anything of note or value here, so feel free to skip forward a couple of paragraphs while I ramble.

It should come as no surprise to anyone that, contrary to common assumption, not all public information is available on the internet - a lot of it is still locked up in those paper things that we call "books" (or printed journals, or what-have-you). This is becoming a serious issue in a time when, for so many people, a search for information begins and ends with Google and anything that a search engine doesn't find is treated as if it doesn't exist. That particular problem, however, is a topic for another day. The point that I specifically wanted to raise is that some topics remain unusually under-represented online. Malacology is one of those mysterious absences. Or, to be more accurate, framework-level malacology is*. Run an online search for, say, Mitridae or Fossarinae or Stomatella, and you'll get a ton of pretty pictures of their shells, but it's surprisingly difficult to find out what they actually are. What features, specifically, maketh a mitrid? What defines a Diodora? I've done a few Taxon of the Week posts on gastropod families or superfamilies by now, and to be honest I've usually ended up blabbing on madly about any old guff in a desperate attempt to hide the point that all I really know about the taxon in question is its name (not being a malacologist myself, I have very little idea where to start looking to find out**). So why is there this particular pot-hole in the information superhighway? These are not obscure, unfamiliar animals. They are large, often cosmopolitan taxa, familiar to many a beach-goer or amateur shell collector.

*If anyone knows of any useful sites, I'd be happy to know about them.

**So why do I write about these things if I don't know anything about them? Because, to be honest, I'm writing these posts for my own benefit and to teach something to myself, not to you. I may not have known anything whatsoever about clausilioids before I started writing a post on them, but hopefully I knew just a little bit more when I'd finished. And if any of you benefited from my learning curve, then that's just the gravy.


Mesomphix andrewsae (Gastrodontidae). Photo by slapcin.

I wonder if the nature of malacology itself is a factor. Perhaps more than any other branch of zoology (with the closest competitor probably being ornithology), malacology has been a field where the Interested Amateur been able to make a prominent contribution. Arthropods are too fiddly, vertebrates start to smell after a few days, but shells are accessible to all (and they're pretty!). This has had a couple of effects on how malacology has developed. One is that molluscan classification was up and running largely before other zoologists had even cottoned on to this new-fangled "family" concept. Another is that books rather than journal articles have held a lot more significance as malacological sources - encyclopaedic works such as Powell's New Zealand Mollusca (just to name one that I'm personally aware of) that were of great appeal (and accessibility) to professionals and members of the public alike. And the thing is, geriatric and dog-eared as some of these of these sources have become, they're still useful today. The reason so little of the information has been transferred online is probably just because, so far, not many people have seen the need to.

Anyway, enough of that, on to the actual topic of this post (and if you did slog through the last couple of paragraphs, a quick reminder that I have absolutely no idea about anything in there, and was almost certainly talking completely out of my khyber). Gastrodontoidea are an assemblage of land snails recognised by Hausdorf (1998) as including six families - Pristilomatidae, Chronidae, Euconulidae, Trochomorphidae, Gastrodontidae and Oxychilidae (the names of two families have been corrected to the names used by Bouchet et al., 2005). Previously these families had been included in the Limacoidea, which Hausdorf divided up into a number of superfamilies. However, he did not dispute the monophyly of the original extended Limacoidea, and many authors continue to use the larger grouping rather than recognising Hausdorf's subdivisions.


Geotrochus obscura (Trochomorphidae). It does not take much to realise how these creatures got their name, does it? Photo from here.

Hausdorf's analysis is not without its problems. For a start, he was coding families rather than individual species, which (a) assumes that the families you're using are monophyletic, and (b) usually requires the author to estimate the 'ground-state' coding for a family, which can be a hazardous exercise (just because the majority of members of a family possess a particular character state does not necessarily mean that state is ancestral for that family). Secondly, the characters that supported monophyly of Gastrodontoidea were reductions of the stimulator in the male genitalia (among other things, the stimulator is the part of the genitalia that produces the love darts in those snails that have them ) and of the venation of the lung. Not only are reductions or losses always somewhat suspicious as supporting characters - if it is easier to lose a character than to gain it, they will probably be prone to homoplasy - but each one of these characters was both homoplastic with other non-gastrodontoid limacoids, and had been reversed in some supposed gastrodontoids. Hausdorf's Gastrodontoidea was not monophyletic in the molecular analysis of Wade et al. (2006) (but pretty much no relationships within the extended Limacoidea were well-supported in that analysis), nor did it appear in the morphological tree of Barker (2001) (which, however, did not include support levels for any of its results).

Most 'gastrodontoids' seem to be rather small (often only a few millimetres in diameter). Many limacoids have small shells compared to their bodies, and are unable to fully retract into them (Bouchet & Abdou, 2001). The Microcystinae, a subfamily of the Euconulidae (though Hyman et al., 2007, suggested they may be closer to the Trochomorphidae), are ovoviviparous - that is, they incubate their eggs internally until they hatch out and are released as live young*.

*Is there a better way of putting this? I just realised that the phrase "live young" is a bit unfortunate - after all, it's not as if eggs are dead.


Euconulus fulvus (Euconulidae). Photo from here.

Gastrodontidae and Oxychilidae possess a cartilaginous love-dart, but other families are dart-less. Gastrodontidae also possess an internal duct between the male and female parts of the reproductive system (remember, all pulmonates are hermaphrodites), and are apparently able to fertilise themselves. Indeed, Barker (2001) lists gastrodontids among families of snail for which some individuals lack the male penis, so they are only able to fertilise themselves or be fertilised by others, not fertilise others. I find this intriguing, as explanations for the ways and means of hermaphroditism often seem to proceed on the assumption that, because of the different required reproductive commitments, 'tis preferable to fertilise than be fertilised (love-darts, for instance, are thought to have evolved to prevent one partner from fertilising the other, then taking off before it is able to be fertilised itself). Penislessness in gastrodontids would seem to go against that assumption, so why would it develop? Is it that, what receptive-only individuals lose in the ability to produce more offspring, they gain in having more control themselves over how those offspring are provided for?

REFERENCES

Barker, G. M. 2001. The Biology of Terrestrial Molluscs. CABI.

Bouchet, P., & A. Abdou. 2001. Recent extinct land snails (Euconulidae) from the Gambier Islands with remarkable apertural barriers. Pacific Science 55 (2): 121-127.

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.

Hausdorf, B. 1998. Phylogeny of the Limacoidea sensu lato (Gastropoda: Stylommatophora). Journal of Molluscan Studies 64 (1): 35-66.

Hyman, I. T., S. Y. W. Ho & L. S. Jermiin. 2007. Molecular phylogeny of Australian Helicarionidae, Euconulidae and related groups (Gastropoda: Pulmonata: Stylommatophora) based on mitochondrial DNA. Molecular Phylogenetics and Evolution 45; 792-812.

Wade, C. M., P. B. Mordan & F. Naggs. 2006. Evolutionary relationships among the pulmonate land snails and slugs (Pulmonata, Stylommatophora). Biological Journal of the Linnean Society 87 (4): 593-610.