Read some biology today; it’s good for you!
It’s not often that a new animal phylum has been described, but a new paper in PLoS ONE apparently does just that, basing the phylum on two enigmatic species, dredged up from the deep sea, that can’t be placed in any existing phylum. This may add one more to the 35 phyla that already exist (see the list here, and please look. It’s nice to review the major divisions of life.)
The paper is by Jean Just et al. (all authors are from the Natural History Museum of Denmark at the University of Copenhagen), and the reference and pdf, which is free, are below.
What we have is something that looks like a cnidarian (jellyfish, corals, and sea anemones) or a ctenophore, but with a stalk. (Some cnidaria do have a stalk). But it has features that keep it from being placed in the phyla Cnidaria or Ctenophora. Its placement on the tree of life is further complicated by two things: we don’t really know where some major groups fit on the tree of life already (see below), and we don’t have any DNA or molecular data from this group to see what it’s most closely related to, or whether it’s an outgroup (a more distant ancestor) to all metazoans (multicellular animals).
The problem is that these creatures, which I’ll show shortly, were dredged up off of Victoria, Australia in 1986 from 400-1000 meters down. They were then fixed in formalin and later transferred to 80% ethanol. I’m no molecular biologist, but I think that would pretty much destroy the DNA, preventing any molecular analysis. And the samples are now old, shrunken a bit and degraded, and so some features may be effaced.
What we have are two species placed in a new genus, Dendrogramma, which the authors consider members of a new phylum as well, though they didn’t formally name one in this paper—probably because the placement of these creatures is uncertain. Two species were named. Here’s the first, Dendrogramma enigmatica:
Like the other speciers, it has a flattened disc with a notch in it, a stalk (so it was attached to the substrate), and a mouth-like opening that leads into an “gastrovascular” canal in the stalk that also feeds into the radiating canals in the disc. The tissue types were not examined, so we can’t draw homologies between the types of layers and those of other metazoans. Here’s the other species, Dendrogramma discoides:
And both species together. You can see from the scale (1 mm) that they were very small (10 mm = 1 cm, and there are 2.54 cm per inch).
Because of the stalk and the inflexible disc, these things were probably unable to swim but attached to rocks or the sea floor. Given their mouthlike opening, the authors suggest that “they fed on microorganisms, perhaps trapped by mucus from the specialized lobes surrounding the mouth opening.”
Why aren’t they members of existing phyla like cnidarians and ctenophores? Because they lack features found in those phyla. As the authors say (my emphasis):
Dendrogramma shares a number of similarities in general body organisation with the two phyla, Ctenophora and Cnidaria, but cannot be placed inside any of these as they are recognised currently. We can state with considerable certainty that the organisms do not possess cnidocytes, tentacles, marginal pore openings for the radiating canals, ring canal, sense organs in the form of e.g., statocysts or the rhopalia of Scyphozoa and Cubozoa, or colloblasts, ctenes, or an apical organ as seen in Ctenophora. No cilia have been located. We have not found evidence that the specimens may represent torn-off parts of colonial Siphonophora (e.g., gastrozooids). Neither have we observed any traces of gonads, which may indicate immaturity or seasonal changes. No biological information on Dendrogramma is available.
Given the absence of DNA data or complex characters that might help us decide where these things fit in the tree of life, the authors can only speculate. One big problem is that we don’t really know where the major phyla of multicellular animals fit on the tree. For example, some biologists claim, based on both molecular and morphological data, that the “outgroup” (the most unrelated phylum) to all metazoa is the Porifera (sponges). Others (and the authors of this paper take this position) claim that the outgroup is really Ctenophora (which, based on morphology alone, I would have thought were more closely related to the cnidarians, as biologists once thought [they’re really distantly related groups, though]). So here’s the phylogeny presented in the paper, showing cetophores as the outgroup to other metazoans (including the Bilateria, the group of phyla that includes all bilaterally symmetrical animals, including us:
To hedge their bets, the authors have also included ctenophores within other groups, as its placement is uncertain. They’ve put Dendrogramma as either an outgroup to all other phyla, or perhaps more closely related to the ctenophores or cnidarians. We just don’t know yet.
Molecular evidence could potentially resolve the placement of all these groups, and, frankly, I’m surprised that we haven’t settled the issue. For Dendrogramma we clearly need fresh material to get DNA (the authors plead for someone to get more specimens), but we could get plenty of DNA from the other species. Either that hasn’t been done (which I strongly doubt), or the lineages diverged so long ago that DNA evidence is inadequate to settle the question of, say, whether sponges or ctenophores are the outgroup. Perhaps some reader can explain to us why this major issue remains unsettled.
I noticed that the discs of these species resemble some creatures described from the Ediacaran fauna (also called the “Vendian fauna”), a group that lived from about 580 million years ago to about 545 million years ago, when the “Cambrian explosion” occurred and Ediacaran animals (if they were animals!) disappeared. (For pictures of various weird Ediacaran creatures, see here.)
My friend Latha Menon, who is not only the trade science editor at Oxford University Press (and editor of the British edition of WEIT) but also a Ph.D. candidate at Oxford’s Department of Earth Sciences, would know more about this, as she works on discs that strongly resemble these, but lived hundreds of millions of years ago. I therefore asked her to relate the new finding to the old group, as they could be related. Her answer is below, along with references. As you can see, she’s a very good writer, and I’m grateful for her input on this issue.
by Latha Menon
The discovery of Dendrogramma from the deep sea off Australia has undoubtedly caused a frisson of excitement among researchers on early life. A living fossil? An Ediacaran that has been surviving quietly in bathyal regions for several hundred million years? Let’s not get carried away, but it is an intriguing find.
When Reginald Sprigg discovered, in the 1940s, a set of strange impressions, many of discoidal forms, preserved on surfaces of the sandstone and quartzite of the Ediacara Hills, South Australia, he called them “medusoids”. Further work by Martin Glaessner and Mary Wade in the late ’60s continued to describe the various discoidal forms as medusoids, while frondose forms such as Rangea were considered to be Pennatulaceans (sea pens), and Dickinsonia was thought to be an annelid. Since then, Ediacaran macrofossils have been found all over the world, including spectacular fossil assemblages from the White Sea coast in Russia, the Nama Group, Namibia, Lantian and Miaohe Formations in South China, and the remarkable “E surface” at Mistaken Point, Newfoundland (see e.g. Fedonkin et al., 2007). The biota gave its name to the Ediacaran Period (635-541 Ma) ratified in 2004, and the fossils themselves appear from about 579 Ma (perhaps earlier), soon after the Gaskiers glaciation, the last of several widespread glaciations, and stretch up to the Cambrian boundary. Close to the boundary, the earliest biomineralized forms, the “small shelly fossils” appear, along with intense burrowing activity (bioturbation), and the Ediacarans, as far as we know, disappear, perhaps in an extinction. So what were the Ediacarans?
Nearly 70 years after Sprigg’s discovery, with many more fossil impressions, the affinities of the Ediacaran biota remain uncertain. Remember, that’s all we have – impressions (and in some cases, carbonaceous compressions) in the rocks. No skeletons; no biomineralized parts; and certainly no DNA. Molecular clocks provide little help so far back in time; results are notoriously varied and unreliable. Fossils really matter. And in spite of the limitations, a great deal of work has been done to glean information from the often exquisitely detailed impressions and the sedimentology of the surrounding rock, which indicates the setting in which they lived and died. As more evidence accumulated concerning morphology and sedimentary context, the early interpretations of medusoids, pennatulaceans, and annelids was increasingly questioned. Some may reach 30 cm and more in size, but were they necessarily early animals? The late Dolf Seilacher proposed that these enigmatic forms represented a “failed experiment”.
Discoidal forms are particularly hard to interpret. Some simple forms may be pseudofossils formed by physical processes; others have been persuasively explained as microbial colonies (Grazhdankin and Gerdes, 2007). Still, some possible affinities with familiar taxa have been suggested, with evidence put forward for bilaterian traces from about 555 Ma, and the claim that Kimberella may have been an early mollusc (Fedonkin & Waggoner, 1997). Our own group has found evidence in the early Ediacaran Avalon assemblage of Newfoundland for horizontal and vertical motion associated with a discoidal form (Liu et al., 2010; Menon et al., 2013), suggesting that some of these discs may indeed have been simple polyp-like forms. Two weeks ago, we published a paper describing Haootia quadriformis n. gen. n. sp. (Liu et al., 2014: – an extraordinary fossil impression that appears to indicate muscle bands, and bears a striking similarity to modern stalked jellyfish (Staurozoa). The idea that some of the Ediacaran discoidal forms may have been stem-group medusoids has made a big come-back.
And then we hear of Dendrogramma. The authors have referred it to Metazoa incertae sedis [“of unknown placement”]. The organism resembles cnidarians and ctenophores, but lacks the characters to establish a certain affinity with either group, though molecular analysis of further individuals might yet show that it belongs to one of these lineages (the existing specimens were damaged in preparation and not suitable for DNA analysis). Whether or not Dendrogramma turns out to represent a new phylum, it does seem to be a relatively primitive form, lacking cnidocytes, colloblasts, and other more sophisticated characters. From the discription, Dendrogramma appears to be a simple diploblastic animal with a disc showing a distinct pattern of gastrovascular branches and, in the case of one of the two species, D. discoides, a stalk with a possibly trilobed mouth-field. Various Ediacaran discoidal forms, particularly those from the diverse assemblages of South Australia and the White Sea, Russia, have trilobed structures within the disc, most obviously Tribrachidium. The authors point out the similarity of D. discoides with Albumares brunsae, and Anfesta stankovskii, as well as the less obviously trilobed Rugoconites from South Australia. There does appear to be a morphological similarity, particularly with the former two forms, both in the trilobed structure and in the pattern of radial ridges compared with the gastrovascular branching on the disc of Dendrogramma.
So can we conclude that Dendrogramma is a living Ediacaran? That’s almost certainly going too far. But it does seem quite possible that some of the trilobed Ediacaran discs may represent stem-group forms of such a lineage, lacking in such modern armoury as cnidocytes (for what would they sting?) and possessing a simple small mouth with no surrounding tentacles. As for all the other kinds of Ediacaran forms, even the many other discoidal forms, well, the work goes on.
Latha’s References:Fedonkin, M.A., et al. (eds), 2007, The rise of animals: Evolution and diversification of the Kingdom Animalia: Baltimore, Maryland, Johns Hopkins University PressFedonkin, M.A., and Waggoner, B.M., 1997, The late Precambrian fossil Kimberella is a mollusc-like bilaterian organism: Nature, v. 388, p. 868–871Glaessner, M.F., 1959, Precambrian Coelenterata from Australia, Africa and England: Nature, v. 183, p. 1472–1473Glaessner, M.F., and Wade, M., 1966, The late Precambrian fossils from Ediacara, South Australia: Palaeontology, Vol 9 (4), pp. 599-628Liu, A.G., McIlroy, D., and Brasier, M.D., 2010, First evidence for locomotion in the Ediacara biota from the 565 Ma Mistaken Point Formation, Newfoundland: Geology, v. 38, p. 123–126Menon, L.R., McIlroy, D., and Brasier, M.D., 2013, Evidence for Cnidaria-like behaviour in ca. 560 Ma EdiacaranAspidella, Geology, v. 41, p. 895–898Sprigg RC. 1947. Early Cambrian (?) jellyfishes from the Flinders ranges, South Australia: Trans. R. Soc. S. Aust. 71(Pt. 2):212–24
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REFERENCE TO THE NEW PAPER: Just, J., R. M. Kristensen, and J. Olesen. 2014. Dendrogramma, New Genus, with Two New Non-Bilaterian Species from the Marine Bathyal of Southeastern Australia (Animalia, Metazoa incertae sedis) – with Similarities to Some Medusoids from the Precambrian Ediacara. PLOS One DOI: 10.1371/journal.pone.0102976
“I noticed that the discs of these species resemble some creatures described from the Ediacaran fauna”
Just what I was thinking before I scrolled down to see that you’d arrived at the same conclusion!
If they *are*, and turn out to be nested within basal Metazoa that will be a nice kick in the butt for the creationists.
I read the biology and is IS good for me. I can feel my sertonin uptaking and my LDL falling.
All those gastrovascular branches are puzzling. Why would it need so much processing of food? Or is that a replacement for a vascular system?
I like the pictogram of Bilateria – a person at a desk with a laptop.
A huge gastrovascular component could reflect an enormously primitive/inefficient digestive system.
A lack of differentiation between digestion and the distribution of the resources….or a rather different approach to the problem.
The paper describes the stalk as a pharynx with a terminal mouth. Is this consistent with attachment to a substrate?
Having the mouth down on the substrate does seem weird but maybe they feed on organic ooze. They could extend the stalk into the ooze, and probe around with it while keeping the flat disc on the sea surface.
The digestive anatomy reminds me of that of flatworms. They have a tubular opening to the digestive tract that is called a pharynx, leading to branching, blind ended gastrovascular branches. Flatworms of course just stay on the substrate, probing their pharynx into the ooze on occasion, and they crawl around.
Actually, this makes me wonder if these are not just simple, disc-like flatworms. Being dredged up to a low pressure environment and then popped into formalin which will cause distortion and the formalin will cause a lot of shrinkage of the most delicate parts. Maybe these are just very shriveled flatworms. Hmmm.
After talking to Latha, I’m not so sure they’re sessile after all. Yet the authors say in their paper that they weren’t free swimming because the disc was rigid. I’m confused.
Maybe the authors are envisioning the “holdfast” (if that is the term) using mucus for both functions, as anchor and by later absorption feeding: “they fed on microorganisms, perhaps trapped by mucus from the specialized lobes surrounding the mouth opening.”
Maybe they don’t mind being loosened during an absorption phase.
Or we are placing the creature, if that is what it is, upside down. It happened to some Cambrian creatures…
But the disc seems pretty much a swim device in my eyes, flatworm or not, presumed rigidity or not.
I’m confused.
What if the mucus can be used as a conveyor belt though? Secreted in the outside lobes, absorbed by the central mouth, providing both adhesion/suction and feed?
I was thinking that it needed tight regulation, hence my suggestion of two phases instead, but perhaps not.
Squishy invertebrates can use cilia and mucus to convey trapped food (bacteria and decaying organic stuff) to a mouth. So maybe.
But that would not explain why they have a stalk. Why transport farther than necessary?
No cilia were found inside or outside, but not sure if this could be a preservation artefact. These specimens have been through nearly as much physico-chemical abuse as Ediacaran fossils.
Let’s hope they haven’t gone extinct since 1986. Two species, what are the odds of losing both?
If this turns out to be a new phylum I’d go with the name ‘Basidiozoa’ ( because it looks like a mushroom) but I’m guessing it wont be. I think its a secondarily reduced cnidarian.
I think it was a bit premature to compare these to extinct forms but it was good PR. Now the headlines can be: “Extinct Creature from Precambrian Found Alive”
Nobody is saying they’re part of that extinct group, but they could be. It would in fact be remiss NOT to draw the parallel, because they might be descendants of the Vendian fauna. Nobody, after all, is proclaiming, “Edicaran animals still with us.”
I know. I was just saying they could have given science journalists and excuse to go wild.
I was pleased to read the piece by Latha Menon. I’ve been giving my students my opinion for years ( and making it clear it was my opinion) that the ediacarans were stem cnidarians. I wouldn’t be surprised to learn that the ediacarans were all living in symbiotic associations with algae – like corals, Chlorohydra and Cassiopeia- and that cnidocytes and predation came much later.
It’s true the authors don’t claim to have found a new phylum or an extant Ediacaran, but their statement in the Abstract that “Resolving the phylogenetic position of Dendrogramma depends much on how the basal metazoan lineages (Ctenophora, Porifera, Placozoa, Cnidaria, and Bilateria) are related to each other” (repeated in the Discussion) implies that they think Dendrogramma is not a member of one those other lineages but is a sister group to one or more of them instead. That statement seems too strong. Quite a few new “phyla”, especially things with small bodies and simplified anatomy, turned out to be miniaturized members of some other phylum.
A commenter at the PLoS ONE site proposed that these might be flatworms with a large evertible pharynx (the ‘stalk’) connected to a flattened disc-shaped body including the many canals of the gut (as Mark S. also proposed @ 3 above). It doesn’t seem to be a possibility that the authors considered (at least not in print in the paper). If Dendrogramma is just an unusual flatworm then it will not be necessary to resolve the deepest parts of the animal phylogeny in order to know who Dendrogramma’s closest relatives are.
I like the tree reference in the new name. 🙂 The look tree-like.
Formalin fixation does indeed cause big problems with subsequent attempts at DNA analysis, and subsequent exposure to ethanol apparently wrecks the train yet further. <a href=http://books.google.com/books?id=n8J_BLagCAgC&pg=PR21&lpg=PR21&dq=formalin+adenine+reaction&source=bl&ots=vtvrxEgOTn&sig=fEQBZboRHkr0zCsTMBV0tZ4nuYw&hl=en&sa=X&ei=FWwMVO2UH_iCsQShz4D4Dg&ved=0CEMQ6AEwBQ#v=onepage&q=formalin%20adenine%20reaction&f=falseSome sense/details of that here.
‘Formalin’ will have a lot of methanol in it, so if that causes problems like ethanol then the train is wrecked.
Makes you wonder how species are started to be archived today, seeing these problems. If sequencing isn’t planned, are genome sample bits set aside, assuming formalin is still the best preservation?
And how do one guarantee a genome “holotype” (at the very minimum), preferably without human and bacterial contamination?
A tissue sample could contain some human DNA and a lot more DNA from the resident bacteria. But the vast bulk of the DNA will be from the target specimen. I have never done this, but I still would expect that the DNA that is amplified by PCR will be overwhelmingly from the specimen. Of course when it is compared to other DNA we will expect it to not match our species, or of bacteria.
Sure, I was thinking of minimizing contamination and maximizing resolution (no confusing genes).
But reading your comment, I also realize one need to make sure bacteria (and fungus) are dead. Cold storage, then.
Or if not dead, at least sufficiently inert.
I was following this story as well, and my 1st thought was that these looked like some of the Ediacarans.
Another possibility to at least keep in mind is that these are fancy bacteria colonies. Bacteria can form colonies of surprising complexity. Right now I think that is less likely, given the reliable connectivity of the ‘gastrovascular branches’. The 1st species shows a pretty good periodic pattern of gv branches as you walk along the circumference. So ‘that’s no bacteria colony!’
Could someone please go out there and dredge up more of these? We need the DNA. Thks.
Upping anchors … oh, sorry, the anchors are already up. We’re on DP.
But it’ll take several weeks to steam round to Australia.
Maybe I’ll just hang around the ROV shack a bit more and see if there’s anything interesting to see on the seabed. Trouble is, if we do find something interesting, we just move to an alternative spud location.
I work with Formalin-fixed tissue all the time. It is an excellent fixative for preserving DNA IF the tissue is embedded in paraffin within a relatively short time, say a few days. Prolonged exposure to Formalin, or pretty much any other fixative, gradually degrades both DNA and proteins. The lag time here, which seems to have been many years, with a transfer to alcohol along the way, pretty much means that there is no chance of getting usable DNA from these specimens.
I like these weird animals. Some of the living ones can be very pretty – Alexander Semenov photographs them in the White Sea (brrrr). Jerry posted pictures of his worms before. He & some biologists will be studying gelata on a 3 year expedition.
Thanks for an engaging article!
Speaking as a layman, with a peculiar reading of that one fancy, my limited understanding was that sequencing new groups is a major undertaking. The new genes must be identified as such (“annotation”, I take it), preferably identified to function, et cetera. E.g. I think Placozoa has been sequenced repeatedly, where the first sequencing had poor coverage (which I take is more like 50 % of genes rather than 100 %), and so poor annotation.
That said, the sequencings of ctenophores seem to agree on its placement as the sister group to the rest of the Metazoa. These are the two I know of:
#1: “The Genome of the Ctenophore Mnemiopsis leidyi and Its Implications for Cell Type Evolution”, Joseph F. Ryan et al., Science 342, (2013); “My Oldest Sister Is a Sea Walnut?”, Antonis Rokas, Science 342, 1327 (2013).
“Our phylogenetic analyses suggest that ctenophores are the sister group to the rest of the extant animals.”
#2: “The ctenophore genome and the evolutionary origins of neural systems”, Moroz et al, Nature (2014).
“Our integrative analysis place Ctenophora as the earliest lineage within Metazoa.”
As a layman, one has no reliable access to the consensus. Maybe the above isn’t enough, maybe the process of acceptance hasn’t finished, et cetera. The last paper would make neural and muscular systems as convergent evolved at least twice, I think. It also claims, roughly, that there is an “apparent absence of HOXgenes” among other absences, somehow organizing the development of the young ctenophore anyway. (As I understand it the most stem-ward ctenophores are alike as larvae and adult.) It is a hefty bit to chew on, I’m sure.
As a personal note: If ctenophores are the sister group to the rest, and later Edicarian impressions include sponges, ctenophores naively seem to sit well close to fractal-like rangeomorphs. None had the body plans that a later Metazoa had.
Maybe Hox type body plans didn’t evolve until around the time the ancestors to Placozoa emerged?
“Ediacaran impressions”.
Speaking of fractal-like rangeomorphs and the putative absence of Hox bodyplans in a Dendrogramma. FWIW, I just noticed that the radiating disk canals in both species are branching fractal-like.
Not uncommon elsewhere perhaps. But suggestive here?
I am surprised abt. the claim that the ctenophores seem to lack HOX genes, but that is perhaps one reason why they might be an outgroup of the metazoa. So they could be an outgroup, or a ‘degenerate’ in-group that has lost their HOX genes.
Funny, the first paper says nothing on HOX genes what I can see. They looked at cell signaling mostly. Well, considering the then rather newly sequenced Porifera and its interesting basic cell signaling, that was probably most urgent as I remember it.
On your idea: I agree on the possibilities in/outgroup, but I think the “degenerate” hypothesis is the most complex one.
Is the hypothesis that earlier metazoa evolved HOX genes, then ctenophora lost them, then ctenophora somehow evolved a new way to organize development? And how do we place Porifera against that?
Ctenophores are very organized compared to Porifera. Maybe it is Porifera that would more easily fit the bill of “degenerate”?
Now me, I seem to evolve an headache… =D
By the way, I found something (in paper #1) that add a little more detail to what I said earlier:
“We assessed two data matrices that differ in breadth of taxon sampling and fraction of missing data: a “Genome Set” that includes only data from complete genomes (13 ani-
mals, 19.6% missing data) and an “EST Set” that includes partial genomic data from many taxa (58 animals, 64.9% missing data).”
So either way we cut it, I think that by 2013 there was about 30-40 % of the data that ought to place 30 phylums based on genome sequencing alone. And I guess you would rather like to have 2-3 species, with good coverage so a good number of repeats on each species, for every phylum.
They could use the data to try to field specific questions though. E.g. ctenophores, in- or outgroup.
Complex organisms can build bodies with axes without relying on HOX genes. The plants do that. Since HOX genes tend to be clustered, it might not be too hard to lose all of them. I agree, though, that it is less parsimonious to have had HOX and then lost them, rather than to never have never had HOX at all.
‘Tis better to have Hoxed and lost
than never to have Hoxed at all.
TYTY (Tennysoned that for you)
(That should obviously be TTFY)
Seems to me that we should be approaching the point where we can start to make educated statistical guesses about how many more groupings at all levels, not just phyla, we should expect to discover. There are forms of math that, as I understand it, are good at that sort of prediction.
b&
The problem is that most ‘levels’, including that of phyla, are not real. The Linnean hierarchy of KPCOFGS is coherent in the sense that each species is contained in successively more inclusive genus, family… kingdom, but if you want to start counting families or kingdoms you need to further assume that Family A (of arthropods, say) and Family B (of birds) are the same sort of group as Family C (of whales) and so on. This is obviously wrong, because any taxonomist is free to revise a group and decide to add or subtract or interpolate new levels (locally) without those effects rippling across the entire classification of life (e.g. what were elapine colubrid snakes in the 19th century are now several families within Elapoidea; Serpentes and Lacertilia used to be separate orders, but now we know snakes are deeply nested within the lizard tree). Even ‘species’ are not really comparable, when you consider parthenogenetic organisms, genetically distinct but morphologically indistinguishable sibling species, and widespread polytypic species.
There have been a lot of useful studies done (e.g. in palaeontology) by counting species, genera, families, orders etc., without necessarily acknowledging these unrealistic assumptions. All results of that (e.g. the rough outlines of the big five mass extinctions) have had to be revised constantly with new taxonomy.
That said, you can apply a catch-per-unit-effort approach to get a species accumulation curve and calculate an asymptote, either for a single research project and locality, or (in principle, I suppose) for the whole of life on earth. Of course, some mathematical models work just fine with invalid assumptions and poor data…
Thanks for that! Much appreciated.
b&
Reblogged this on macrocritters.
Midi-critters, surely?
.
The properly terminated name is enigmaticum, as the gender of the generic name Dendrogramma (and others ending in gramma) is neuter. See, for example, Roland Brown, 1956. Composition of Scientific Words.
Don’t you hate it when they do that?
There is no specific mention of the gender of Dendrogramma in the paper, so correcting the species name ending is a trivial change that doesn’t even count as a nomenclatural act under the Code. Unless you read a different section of the Code first, that seems to say such corrections are not required…
I don’t have a copy of the code handy, but agreement in gender of adjectival species names with that of the genus is a requirement. The authors didn’t mention the gender of the generic name, but it is obvious that they presumed it to be feminine by the ending they used for the specific name. Most generic names that end in a would be feminine, except that a majority of those ending in ma happen to be neuter. Most likely they didn’t bother to check. Whether or not it ever gets used, the correct name is enigmaticum.
It’s a really interesting paper, but I’m not totally convinced that what they describe isn’t just a series of detached fragments of some larger (and already known) organism. I work in deep-sea biology and have personally worked through an awful lot of sediment samples from the depth range these things came from. Some of my colleagues have worked through even more. None of us can recall seeing anything quite like this. The problem therefore lies in the fact that at the higher-taxon level, deep-sea animals are very widespread. Without a huge effort by taxonomic specialists you would be hard put to tell the difference between faunal samples from 1000 m depth from, say, the northeast Atlantic, south Pacific or anywhere else. Small animals ( a few mm long) like these things are often very abundant at these relatively shallow depths (yes, to deep-sea biologists, 1000 m is shallow and 400 m is practically high-and-dry!), so I find it surprising that these things haven’t been described before. There has been a lot of work done at these continental slope depths, and I would expect these things to have been noticed before if they were really new at the level these authors suggest. If they are surviving Ediacarans, it seems a bit odd that they should have lasted 600 million years only in one corner of the SW Pacific.
I also read in their paper that these things have been in fixative storage for a long time, and some of them have dried out and been rehydrated. Anyone who works with preserved benthic samples will confirm that this kind of treatment can cause a lot of distortion and specimens can end up looking very different to their life appearance.
As I say, this is a really fascinating description and may yet turn out to be something as novel as the authors suggest. However, I think it might be premature to get too excited right now. We will need more, preferably fresh, specimens, good enough for DNA extraction, to find out what they really are.
With a seabed temperature here of 3.35degC (I had reason to ask the ROV pilots for a reading a couple of days back) and a single-digit latitude, it is a very homogeneous, widespread environment. So I’d doubted that the species would be restricted to the given locality too.
Paddling pool territory. However with a couple of hammerheads hanging around the vessel (and being annoyingly camera-shy), I can contain my interest in paddling.
I really should spend more time in the ROV shack. Interesting footage.