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February 2016 Archives

Tunicates are more commonly known as 'sea squirts' - little blobby marine creatures that squirt water when you touch them (hence the name). We don't hear about them often, except perhaps when they make the news for all the wrong reasons. But from an evolutionary perspective they are fascinating little creatures - and it's largely due to their larvae.

As an aside: why do we call them tunicates? Because the body of the adult organism is enclosed in an outer sheath, aka a tunic. The majority of tunicate species belong to a group known as ascidians, which as adults live in shallow waters, attached to rocks or maritime structures (including boats). The remainder are planktonic & found out in the open ocean.

The larvae of many ascidians are free-swimming and, because of their body form, are often described as 'tadpole larvae'. (Some of the non-ascidian tunicates have adults with the same morphology.) These little animals have a number of features (shared with creatures such as the cephalochordate formerly known as Amphioxus) that link them with the chordates: a hollow dorsal nerve cord, a post-anal tail, a pharynx with slits in it (which feeds into the gut), and a living cartilaginous rod known as the notochord, against which the animal's muscles work. (The larvae, and the adults of some non-ascidian tunicates, are basically little swimming filtration units.)

In fact, because of their rather simple structure, tunicates have long been viewed as representing the likely common ancestor of both chordates (a group that includes us) and the slightly-more-complex cephalochordates like Amphioxus. However, a newly-published & fascinating article by Linda Holland (2016) looks at 

the highly derived body plans and life styles of the tunicate classes, their importance in the marine food web and their genomics [with an] emphasis ... on the impact of their especially rapid evolutionary rates on understanding how vertebrates evolved from their invertebrate ancestors.

It turns out that a genomic comparison, using nuclear genes from chordates, cephalochordates and tunicates, indicates that it's actually Amphioxus that sits at the base of this particular group. This in turn means that tunicates

have lost a lot of what the long extinct ancestral tunicate once possessed. 

This genomic work is fascinating on a number of levels. For example, the 'textbook wisdom' is only bacteria (ie Prokaryotes) have their genome organised into operons, where a single mRNA transcript contains several genes. But it turns out that tunicates, which have a rather small genome.

[have] a high percentage of genes in operons

something that Holland states they share with roundworms (nematodes) and some flatworms, which apparently also have "reduced genomes". In tunicates, it seems that among the genes that have been lost are some of the 'Hox' genes - genes that control the development and patterning of body form. 

I learned heaps of new things from this paper: tunicates are able to regenerate most of their bodies, for example (makes sense, I guess, as the sessile adult sea squirt can't exactly avoid being snacked on by predators). Apparently this is achieved by pluripotent stem cells in the animals' blood, though how it's done is still something of a mystery. And I had no idea at all that the animal's 'tunic'

contains cellulose, synthesized by a cellulose synthase that was evidently acquired in an ancestral tunicate by horizontal gene transfer from a bacterium. 

An animal that produces cellulose! Nature never ceases to surprise :)

L.Z.Holland (2016) Tunicates. Current Biology 26: 4 pR146–R152 DOI: http://dx.doi.org/10.1016/j.cub.2015.12.024

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This is an amended re-post of something I first wrote back in 2012.

We're in the lead-up to the start of the A semester & lately I've spent a lot of time lately advising students on their programs of study. (Consequently I'm a bit short of the time needed to give attention to serious posts on Serious Subjects.) One of the things we often talk about is which major(s) a student should study, where a 'major' is the subject that they will devote most time to over the second & third years of their degree.

This is an important decision for first-year students as it pretty much determines how they're going to spend much of their study time in the ensuing years, and so we take quite a bit of time to talk about the various options, and I often find myself asking 'where do you see yourself in in 5 years' time? It's serious stuff as you don't want to get it wrong, and sometimes I encounter someone who is just a bit confused by the various majors on offer & how they're structured - but happily I have yet to meet anyone with the views parodied by the good folks at xkcd :-) (Thanks to my friends at Number8Network for passing this on, and yes - someone has already had a go at singing it!)

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So, last night I was asked how hedgehogs mate. 

The obvious answer was, carefully! My interlocutor suggested that perhaps face-to-face was most likely, but as far as I know, very few species (& that short list includes our own) do that. It turns out that care is indeed needed, for the male approaches the female from behind, & she must adopt what's coyly called a 'special posture' and flatten her spines so that the sensitive portion of his anatomy doesn't take on the appearance of a kebab.

The question was actually part of a wider discussion around the architecture of sexual reproduction: the mechanics of how the bits fit. If you'd like to hear the entire thing, it's here on the RadioLive site.) Entomologists, in particular, seem to spend quite a bit of time studying this architecture, not least because these details may help them distinguish between species that are otherwise pretty much identical in their appearance. (There's a lovely story about Michael May's work on dragonflies here, complete with etchings illustrations.)

In many cases the structures - which can be quite bizarre - are driven by competition. Competition between the males, but also between males and females. So in those dragonflies, for example, the males' penes have all sorts of features that are related to sperm competition - they allow a male to scoop out, scrape out, or otherwise displace semen deposited by another male, and replace it with their own. And in mallard ducks, which are highly promiscuous, a sort of male/female arms race has driven the evolution of extremely complex genital anatomy in both males & females, discussed here by Ed Yong. Incidentally, that link also includes a video - perhaps not for the faint-hearted! - of the rather explosive uncoiling of & ejaculation from the drake's corkscrew penis.

Some of these structures can be rather large: we're talking a metre long for male African elephants, for example (according to wikipedia), around 2.7m in right whales, and up to 3m in Blue whales (the largest animals alive). And as one might expect, this has been attracting human attention for a long, long time. Sadly, some of that attention has been seriously harmful to the survival of some species - witness the aphrodisiac claims made for the sex organs of tigers by Traditional Chinese Medicine, for example. But there's also the point-&-wink sort of interest, shown in a painting of a dead sperm whale dating from 1606 and described by Menno Schilthuizen in the excellent book, Nature's Nether Regions:

On an otherwise nondescript Dutch beach likes the Leviathan, its beak agape, its limp tongue touching the sand. A smattering of well-dressed seventeeth-century Dutchmen stand around the beast. Prominently located, and closest to the dead whale, stand a gentleman and his lady. With a lewd smile, face turned towards his companion, he points at the two-metre-long penis of the whale that sticks out obscenely from the corpse. Centuries of smoke-tanned varnish cannot conceal the look of bewilderment in her eyes.

These few square feet of canvas ... [exemplify]... the unassailable fact (supported by millenia of bathroom graffiti, centuries of suggestive postcards, and decades of internet images) that humans find genitals endlessly fascinating.

However, it's only relatively recently that this fascination has really been reflected by scientific interest: interest in the structures, their function, and their evolutionary history. But, as Brian Switek points out in his book My Beloved Brontosaurus (which is also an excellent read), we still have no idea how dinosaurs - especially the big ones - actually mananged to mate. Particularly the big spiny ones. This may well remain one of life's not-so-little mysteries. 

 

It has occurred to me that the search history on my computer will look really, really odd as a result of doing a spot of research for this post!

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Demodex mites are tiny little creatures that live in mammals' hair follicles. I first heard about them years ago, when I watched a documentary with my science class back at PN Girls' High. It was about animals that are parasitic on humans, and after the segment on eyelash mites, I don't know about the girls but I felt itchy for days!

For eyelash mites live where the name suggests, in the follicles of our eyelashes. (There are 2 species: Demodex folliculorum and D. brevis.) The common name gives an idea of just how small they are: adult length is 0.3 to 0.4 mm. They spend a lot of time inside the eyelash follicles, snacking on the sebum and dead cells (or maybe the bacteria) that accumulate there. But at night... at night, they come out and wander across our faces as we sleep, achieving a speed of 10cm/hr or more. Which doesn't sound much, but when you remember how small they are, that's quite an achievement. Presumably that's also when they mate, which they do where an eyelash follicle opens to the skin's surface. 

I was surprised to discover that these mites lack an anus. This sounds somewhat problematic, but the eyelash mites have survived, with their human hosts, for at least tens of thousands of years, so they obviously cope somehow. And when they die, their little bodies degrade and release their contents. On your face. Or in the follicles where they spent most of their lives.

Though demodex mites are tiny, there are an awful lot of them. There may be only one or two per hair follicle (they don't restrict themselves to the eyelashes), but an individual human has around 5,000,000 hairs on their body (Thoemmes et al., 2014), so that's an awful lot of available places for a mite to set up home in.

Thoemmes & her co-workers were interested in the genetic diversity of these mites. They predicted there'd be geographically-distinct lineages, because the tiny animals are very closely associated with their hosts and don't seem to be particularly mobile between hosts. However,

if Demodex lack strong geographic structure, it suggests the movement of mites among humans must occur very frequently (perhaps even with social greeting rituals) and across large geographic distances.

To test this hypothesis, the team examined adults (from a single North American population) visually, but also tested skin scrapings for the presence of mite DNA. The results showed that despite being able to see mites on only 23% of their sample population, 16S rDNA sequencing indicated that 100% of those sampled actually had mites present. The latter matched other research showing that 100% of dead bodies tested positive for the presence of Demodex.

Figure 2 from Thoemmes et al. (2014): Maximum likelihood (ML) phylogeny of mites based on 18S rDNA sequences.

While the results of their phylogenetic analysis of the mite DNA are based on samples from only 29 people, they're interesting nonetheless. It appears from that analysis that the 2 species, D.folliculorum & D.brevis, probably colonised humans at different times. Because D.brevis' DNA indicates that their nearest living relatives are mites living on dogs, then the researchers suggest that we acquired this species from our doggy friends, perhaps as recently as 11,000 years ago but possibly as many as 40,000 years ago. There does appear to be some regional variation (based on a comparison of the US data with earlier sequencing results from Chinese populations), but there's also quite a bit of variation within populations, due perhaps to individual humans picking up different mites on different occasions as individual humans came into close physical contact.

And after reading all this & watching a few videos, I feel itchy again!

Thoemmes MS, Fergus DJ, Urban J, Trautwein M, Dunn RR (2014) Ubiquity and Diversity of Human-Associated Demodex Mites. PLoS ONE 9(8): e106265. doi:10.1371/journal.pone.0106265

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Occasionally it's nice to just post a pretty picture. This is one that I took back in July 2015, while we were in France. We'd gone to visit the ruins of of an old Cathar castle called Peyrepertuse and there, on one of the scraggly plants growing on a patch of gravel by the side of the track, was this butterfly. It's a European Swallowtail, and oh how I love the camera in my phone!


Thumbnail image for butterfly  closeup.jpg

 

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A friend recently pointed me (via donotlink - well done, Nicky!) at a post on healthnutnews (which reads a bit like an offshoot of mercola.com - this, it turns out, is hardly surprising). It's a while since I've read anything so full of total nonsense - well, a few days, anyway! 

The post, by one Erin Elizabeth, is a paean to someone called Johanna Budwig & her 'life-saving cancer protocol'. I hadn't heard of this particular person before, & according to Erin, this is because all knowledge of her work has been censored by teh ebil Western medical establishment, along with Big Pharma & the nuclear industry, all of whom would be, like, totally out of a job if everyone followed Budwig's advice. Being curious, I thought I'd check - surely there'd be time for a search before the men in black arrived...

To my complete surprise (I was shocked! Shocked, I say!!!), typing 'budwig protocol' into google brought up 142,000 results. Some, like Cancer Research UK, are obviously trying to repress knowledge of the dietary protocol (or at least, advising that It Doesn't Work), but an awful lot of the others provide recipes, advice, and testimonials about miracle cures.

Not a lot of repression going on there, then.

In fact, the entire post is a concatenation of quackery, woo, & mythinformation. Plus an appeal to authority: 

This German doctor was nominated six times for the Nobel Prize for medicine, which means that it would be wise to take her health work seriously. 

Really? Nominations are secret & by invitation, and nominees need to have a fairly solid body of research under their belt. However, a quick pubmed search didn't come up with anything by Budwig, but did give a number of papers whose authors had looked into this & similarly restrictive dietary protocols and concluded that It Doesn't Work (see here, and here, for example). 

Erin also trots out this standard alt.med cliche: 

Any researcher who found a cure would quickly find himself looking for another job, and at some level, all of them know it.

Here is a simple answer to that particularly offensive statement:

Image via The Credible Hulk and sheeple.

What else do we have?

Cancer is ... a modern man-made epidemic? Apparently so, evidence from antiquity notwithstanding: in the world according to Erin, the reason ancient Eyptians suffered from cancer, for example, was mass heavy-metal poisoning.

Medicine is the 3rd leading cause of death in the United States? Well, that one's easy to check, and it's not correct - you'll find the list here. Erin, could it be that you are being just a leetle creative in your narrative?

Surveys show that most oncologists would refuse their own treatments if they had a cancer themselves? Nope. This is cherry-picking, pure and simple. A 1985 survey about the then-new drug cisplatin, which has significant side-effects,did find about 67% of the oncologists surveyed would be reluctant to use it. A follow-up survey in 1997 found a significant reversal: 64% would now use the drug if they needed it. And why? Because science-based medicine moves on & those side-effects can now be minimised or better controlled, or different drugs may be available.

There's also a misrepresentation of Otto Warburg's work around tumour formation and physiology (work for which he really did receive a Nobel Prize), and the rather startling statement that

The secret to beating cancer is that life-giving breath of God: oxygen.

Apparently all that is needed to cure cancer - any cancer - is to provide cells with sufficient oxygen again. My immediate response was, so why is lung cancer so common, then?

And how do you get your tissues back into that oxygen-rich state? With a rather complicated and restrictive diet, of course!

At least Budwig's patients were spared coffee enemas, but they did get flaxseed oil via the back passage if too far gone to take it by mouth. And champagne was on the list of OK things to ingest!

Frankly, the only reason to repress this nonsense would be to reduce the harm done to people gullible enough, and desperate enough, to invest time and money into following it.

Was that a knock at the door ... ? 

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A while back, my Twitter feed brought up a post with the intriguing title "Prof, no-one is reading you". The article kicks off with the following provocative statement: 

Many of the world's most talented thinkers may be university professors, but sadly most of them are not shaping today's public debates or influencing policies.

Now, them's fighting words, but the authors of the article do have some figures at their fingertips:

Up to 1.5 million peer-reviewed articles are published annually. However, many are ignored even within scientific communities - 82 per cent of articles published in humanities are not even cited once. No one ever refers to 32 per cent of the peer-reviewed articles in the social and 27 per cent in the natural sciences.

And it gets worse:

If a paper is cited, this does not imply it has actually been read. According to one estimate, only 20 per cent of papers cited have actually been read. We estimate that an average paper in a peer-reviewed journal is read completely by no more than 10 people. Hence, impacts of most peer-reviewed publications even within the scientific community are minuscule.

Now, I'd be wanting to know how that estimate is derived; it does sound somewhat arbitrary. But even if the figure were 10 times greater, it's still a bit sad, because there's some fascinating research out there & yet, if the authors of the article are correct, so much of it goes unread. One could argue that researchers should cultivate better relationships with mainstream media, & get their work out in 'popular' form via newspaper stories and radio interviews. 

But the article also suggests that researchers make better use of the social media, among them twitter & Facebook, to communicate with a much wider audience. It's something New Zealand's Science Media Centre staff advocate during their popular mediaSAVVY workshops for scientists. One reason for becoming active in spaces like the twittersphere, say the authors, is that lay people looking for scientific evidence to support (or argue!) a position would be able to find a researcher's quick summary more readily than they could access the full article, especially if it's locked away behind a paywall. 

And given the amount of nonsense & pseudoscience that circulates via the net, it's all the more important that someone looking for a science-based viewpoint is able to find what they're after. I'd really rather not live in a world where snake-oil salesmen hold sway.

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No, it's one of New Zealand's big dragonflies, most probably the bush dragonfly Uropetala carovei, and colloquially known as the "Devil's darning needle" (presumably because of their colour & size).

And indeed, they are large creatures, as you'll see from the photos. The adult dragonfly is the biggest dragonfly in NZ at nearly 90mm long, and with wings spanning up to 130mm. This one is a male - you can tell (if you get to watch one closely) by the appendages at the tip of its abdomen.

I think he'd flown into one of the windows at work, for when we found him, he was just sitting on the road just outside & likely to be squashed by the next car to come along. When I first went to pick the big insect up up, it flapped around a bit and landed on my friend's leg (she was somewhat uncertain about this!), but eventually we shifted it onto a hebe bush away from the paths & road.

The only other specimens I've been able to observe so closely are dead & mounted in zoological collections, so it was quite something to see and (briefly) handle the living animal, and to observe its enormous eyes and powerful thorax & wings.

They really are great, beautiful beasts :)

dragonfly 1a.jpg

dragonfly 2a.jpg

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Once upon a time, I wrote about traumatic insemination in bedbugs. (Those of my friends who are still traumatised by learning about the reproductive habits of various slug species may not wish to follow that link.) Now, two papers just published in Nature Communications describe the results of sequencing & examining the genome of the common bedbug, Cimex lectularius

Bedbugs have probably been with us since humans first lived in caves, where the bugs jumped (possibly literally) from bats to Homo. They're now a widespread human ectoparasite (found on every continent apart from Antarctica) and have developed resistance to the pesticides once used to control their populations. In introducing their paper on their analysis of the C.lectularius genome, Rosenfeld & his colleagues (2016) comment that

There is a limited molecular understanding of the biology of the bed bug before, during and after feeding on human blood, which is essential to their life cycle since bed bugs are temporary ectoparasites, whereby they access their hosts for blood feeding and then seek the refuge of the indoor environment for digestion, waste production and mating.

To increase our understanding of the bugs' life cycle, Rosenfeld's team looked not only at the genome sequence but at changes in gene expression, finding the most pronounced changes occurred after the insect had sucked its fill of human blood. They also found that these changes in expression 

included genes from the Wolbachia endosymbiont, which shows a simultaneous and coordinated host/commensal response to haematophagous activity. 

In other words, gene expression in both host and parasite changes in a synchronous way after the bug has fed. (Just as an aside, Wolbachia is a bacterium that has a significant impact on the reproductive lives of its host.) In the bugs the change could be described as huge: "20% of all stage-regulated genes" showed differential changes in expression after a blood meal.

As you'd expect, the bugs have a number of genes with anticoagulant activity - after all, having blood coagulate in their needle-like mouthparts while feeding would really gum things up - plus other genes associated with blood-feeding. The research team also identified a number of mutations that confer resistance to pesticides such as pyrethroids & cyclodienes, plus others that may underlie metabolic changes that speed up detoxification. Genes that have an impact on the thickness of the bugs' cuticle also have an impact on resistance (also noted by Benoit et al. 2016). 

In the second paper, Benoit and his colleagues (2016) also analysed the common bedbug genome to produce

a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host–symbiont interactions, and several mechanisms of insecticide resistance.

Traumatic insemination involves male bugs stabbing their sexual partners pretty much anywhere on their bodies with a sharp, pointy, penis. It's a habit that can lead to the females picking up a range of pathogens, and unsurprisingly natural selection has driven the evolution of a range of adaptations minimising the physical harm and risk of infection. 

Because the bugs are obligate blood-feeders (haematophagous), their chemosensory system has evolved to allow them to find their particular hosts (ie us). The team observed that the genes involved in this system differed between C.lectularius & the related species that feeds on bat blood, as the 2 species have specialised on different hosts. They identified a total of 102 genes involved in chemosensory pathways, well down on the number found in related bugs (hemipterans) that feed on a range of plant species. (On the other hand, they have a much-expanded repertoire of salivary enzymes, compared to the plant-sucking bugs.)

The bedbugs' specialisation on human blood as their sole food source did have some potential pitfalls, as apparently vertebrate blood lacks some of the micronutrients that arthropods require. And that's where Wolbachia comes back into the story: 

such specialization also drives obligate associations with symbionts, including Wolbachia, that generate critical micronutrients that are deficient in vertebrate blood (Benoit et al., 2016).

Wolbachia does this by providing its host with 

a cocktail of specific B vitamins that are critical for reproduction and development

The research team also found genes encoding proteins (aquaporins) that allow the bugs to rapidly shed the excess water imbibed in a blood meal, and concluded that differential expression of aquaporin genes (and others) allow the bugs to survive periods of starvation and dehydration in between hosts.

In their conclusion, Benoit et al. comment that the wealth of information uncovered by these genomic studies may allow us to move towards an answer to a pressing question: 

What triggered the current bed bug resurgence?

To which harassed travellers would probably add, and how can we bring them back under control?

J.B.Benoit, Z.N.Adelman, K.Reinhardt, A.Dolan, M.Poelchau, E.C.Jennings, E.M.Szuter, R.W.Hagan, H,Gujar, J.N.Shukla, F,Zhu, M.Mohan, D.R.Nelson, A.J.Rosendale, C.Derst, V.Resnik, S.Wernig, P.Menegazzi, C.Wegener, N.Peschel et al. (2016) Unique features of a global human ectoparasite identified through sequencing of the bed bug genome. Nature Communications 7 Article number 10165 doi:10.1038/ncomms10165

J.A.Rosenfeld,D.Reeves, M.R.Brugler, A.Narechania, S.Simon, R.Durrett ,J.Foox, K.Shianna, M.C.Schatz, J.Gandara, E.Afshinnekoo, E.T.Lam, A.R.Hastie, S.Chan, H.Cao, M. Saghbini, A.Kentsis, P.J.Planet, V.Kholodovych, M.Tessler et al. (2016) Genome assembly and geospatial phylogenomics of the bed bug Cimex lectularius.  Nature Communications 7 Article number: 10164 doi:10.1038/ncomms10164

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By now many of you have probably seen images of green-glowing zebrafish, or pigs whose snout & trotters glow in the dark. In both cases the animals are genetically modified and are expressing a fluorescent protein originally sourced from a jellyfish. (The body form of a jellyfish is a medusa, while that of sea anemones & their freshwater relative, Hydra, is called a polyp.) There are a range of these proteins, which collectively belong to a group called the Green Fluorescent Proteins (what else?), and while a wide range of jellyfish produce them1 there are only occasional reports of glowing polyps.

However, in a paper just published in the open-access journal PLoS ONE, Andrey Prudkovsky & his colleagues describe finding tiny (~1.5 mm) fluorescent polyps living in the Red Sea. More specifically, growing in colonies on the shells of small gastropods, a relationship described as epibiotic. The snails are active at night on the sandy seabed, and the researchers noted that the little gastropods buried themselves in the sand when a torch shone on them. They also noticed that the snails, as they moved about in the moonlight, were covered with tiny pinpoints of green light.

Where fluorescence has been described in other polyps, it's mostly been in the 'stalks' of the little animals, but in all the polyps Prudkovsky's team studied, the intense green glow came from a region known as the hypostome - the region around the animal's mouth & encircled by its tentacles. Because both the intensity and the site at which the proteins are expressed is so unusual, the researchers suggest that this could be a useful taxonomic characteristic, given that it's hard to tell one colonial polyp species from another.

They also speculate on the adaptive significance of a polyp having a green glow around its mouth, suggesting that 

[f]luorescence in the hypostome of Cytaeis sp. has probable ecological significance as prey are likely to be attracted to the tentacles and mouth of the polyps

although I do feel that until there's actual observational evidence of this happening, it's a little like an evolutionary just-so story. But isn't the combination of little snails and glowing polyps rather beautiful?

Fig 3.  Hydroid polyps of Cytaeis sp. from the Saudi Arabian Red Sea, scale bar 2 mm; (A) fluorescence of living polyps on the shell of the gastropod Nassarius margaritifer; (B) polyps on the shell of a N. margaritifer specimen, scale bar 2 mm; (C) close-up of polyps, scale bar 0.5 mm.

Fig 3 From Prudkovsky et al., 2016: Hydroid polyps of Cytaeis sp. from the Saudi Arabian Red Sea, scale bar 2mm; (A) fluorescence of living polyps on the shell of the gastropod Nassarius margaritifer; (B) polyps on the shell of a N.margaritifer specimen, scale bar 2mm; (C) close-up of polyps, scale bar 0.5mm. doi:10.1371/journal.pone.0146861.g003

1 And also in comb jellies, marine arthropods, and cephalopods cephalochordates (thanks to herr doktor bimler for picking up the evidence of my brainfade).

Prudkovsky AA, Ivanenko VN, Nikitin MA, Lukyanov KA, Belousova A, Reimer JD, et al. (2016) Green Fluorescence of Cytaeis Hydroids Living in Association with Nassarius Gastropods in the Red Sea. PLoS ONE 11(2): e0146861. doi:10.1371/journal.pone.0146861

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When I was a kid I used to collect shells on the beach - got my Girl Guides 'collectors' badge & everything :) So I really enjoyed reading this post over on Sciblogs NZ. And that in turn reminded me of an article I saw recently on microsnails.

According to that article, 

"Microsnail" is the term for the creatures with shells measuring 5 millimetres or less, sometimes much less (Milius, 2016).

So these are some seriously tiny creatures. According to National Geographic1, microsnails are relatively common (albeit with any given species having a fairly restricted range), but they're just so small that people don't notice them. (NatGeo has an error in the first sentence of that story: I think they meant to say that the snails are a fraction of an inch tall.) However, they are a very diverse group: a 2014 paper on microsnail taxonomy (Jochum et al.) states that snails less than 5mm in length

represent the majority of worldwide tropical land snail diversity. 

The NatGeo story is based on the recent description of 7 new species of microsnail from China, the smallest of which, Angustopila dominikae, could fit in the eye of an ordinary sewing needle: its shell is just 0.86mm long2. Apparently A.dominikae held the mantle of 'smallest land snail in the world' for 5 days, before being knocked off its perch by an even smaller snail from Borneo. 

That there are so many of these tiny species of gastropod shouldn't really come as a surprise: there are more microhabitats available for smaller creatures. (Think, for example, of the tiny eyelash mites that frolic on our faces at night.) But those microhabitats may be limited in extent and that can be a problem (for creatures and those classifying them alike). In the case of the microsnail genus Plectostoma,

many species only occur on a single hill and nowhere else on earth.

And as described in this post on physorg.news

Limestone hills are 'sitting ducks' for mining companies, and many are being quarried away for cement, taking their unique snails  with them to their grave. One species, Plectostoma sciaphilum, is already extinct: its home was turned into concrete around 2003. Similar fates await at least six more species. One of these, P. tenggekensis (named and described in the new paper) occurs only on Bukit Tenggek, which the authors [Liew et al., 2014] forecast to be completely gone by the end of 2014.

Sad to think that these jewel-like creatures may be disappearing from the world even faster than scientists can catalogue them.

Photographs of 17 living Plectostoma species from Liew et al., 2014. Image credit T.-S. Liew.

1 NatGeo has an error in the first sentence of that story: I think they meant to say that the snails are a fraction of an inch tall.

2 Now, if that's their adult size, imagine how tiny the juveniles must be! 

A.Jochum, R.Slapnik, M.Kampschulte, G.Martels, M.Heneka & B.Pall-Gergely (2014) A review of the microgastropod genus Systenostoma Bavay & Dautzenberg, 1908 and a new subterranean species from China (Gastropoda, Pulmonata, Hypselostomatidae). Zookeys 410: 23-40. doi: 10.3897/zookeys.410.7488

T-S Liew, J.J.Vermeulen, M.F.bin Marzuki & M.Schilthuizen (2014) A cybertaxonomic revision of the micro-landsnail genus Plectostoma Adam (Mollusca, Caenogastropoda, Diplommatinidae), from Peninsular Malaysia, Sumatra and Indochina. Zookeys 393: 1-107  doi: 10.3897/zookeys.393.6717

S.Milius (2016) The fine art of hunting microsnails: beauty and sorrow in five millimetres or less. Science 189(2): 4

 

 

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