The first venomous crustacean is found

The phylum Arthropoda contains four major living groups, usually considered subphyla: Hexapoda (insects and a few other groups like springtails), Myriapoda (mostly centipedes and millipedes), Chelicerata (spiders, scorpions, horseshoe crabs, mites, etc.) and Crustacea (crabs, lobsters, barnacles, shrimp, etc.). Trilobites, which are extinct, are classed as another subphylum.

The first three of these living groups all contain species that have venom, which, biologically, are toxins injected into a prey with a bite or sting (delivery via those methods distinguishes venoms from, say “poisons,” as found in some frogs that are toxic to predators). Up to now, though, no crustaceans had been known to have venom.

This has changed with the publication of a new paper in Molecular Biology and Evolution (advance online manuscript; free), by Björn von Reumont et al. The authors show—not definitively, but suggestively—that some remipedes—rare, blind crustaceans that live in marine underwater caves—have venom that they inject into their prey.

Remipedes were discovered only in 1981, and there are only 17 known species. They constitute a class in the subphylum Crustacea. Here is an individual from the University of California’s Museum of Paleontology. Remipedes are about 10-40 mm long: about half an inch to 1.5 inches:

speleon_b

Previous work had suggested that these species could be venomous, as they have biting mouthparts, but this wasn’t investigated. In fact, the going wisdom was that they fed on suspended particles.  But morphological analysis of one species from the Yucatan in Mexico showed a “highly adapted venom delivery apparatus” as well as mouthparts that could deliver venom, and lab studies showed that captive individuals of the species, Speleonectes tulumensis, could indeed capture and kill small prey.  Here are the venom glands and the paper’s caption:

Picture 2

Figure 1 – 3D reconstructions of Speleonectes tulumensis (Crustacea: Remipedia)
from high resolution SR-!CT data.
A) Ventral and B) lateral view showing the course of the venom delivery system
(VDS), (purple) and its position inside the body. C) Anterior and D) posterior view
focused on the maxillule and the muscle equipment related to the VDS.
Abbreviations: 4 seg, 4th segment; 5-7 seg, 5-7th segment; ab, abductors; ad,
adductors; am, anterior apodemal muscle; br, brain; cep, cephalon; dc, ductus; gl,
gland; mxu, maxillule; phx, pharynx; rv, reservoir; t, tentorium; vm, ventral apodemal
muscle; vnc, ventral nerve cord. Images not to scale to each other, mouthparts and
other structures are not shown.

How did they find the venom? They used “transcriptomics,” a newish way of finding the DNA (and protein) sequences of genes that are actually expressed in organisms, that is, whose DNA is converted into RNA. (Remember that a lot of DNA is “junk” that never does anything.)

The authors extracted RNA from the venom glands, sequenced those RNAs by converting them to DNAs and sequencing the latter, and then translated those DNA sequences into protein sequences (the messenger RNA’s are read into proteins). They then looked in databases for proteins corresponding to known classes of venoms.

And they found at least three types of putative venoms, with 108 different forms of those venoms. The three classes are peptidases, enzymes that dissolve protein, chitinases, which do the same for that material, found in exoskeletons, and neurotoxins.  While the authors didn’t actually isolate the venom itself, they did this indirectly by finding sequences that correspond to things known to be venoms.  It remains to be demonstrated that there actually are venoms in these species that kill prey, but the evidence is pretty strong. And the venom proteins seem most closely related to proteins found in spiders.

Here’s the species that was studied:

_70643741_70643631

While the results need confirmation (are those venoms actually used to kill?), the authors suggest that “remipedes can feed in an arachnoid manner, sucking the prey’s liquefying tissue out of its cuticle.”

So there’s your fact for the day, and be sure to drop it at the next cocktail party. “Say, did you know they found the first venomous crustacean?” is sure to bring gasps of wonder and admiration over a round of martinis.

h/t: James

______________

Björn M. von Reumont, Alexander Blanke, Sandy Richter, Fernando Alvarez, Christoph Bleidorn, and Ronald A. Jenner 2013. The first venomous crustacean revealed by transcriptomics and functional morphology: remipede venom glands express a unique toxin cocktail dominated by enzymes and a neurotoxin. Mol. Biol. Evol.: mst199v1-mst199.

16 Comments

  1. Bruce S. Springsteen
    Posted October 24, 2013 at 5:48 am | Permalink

    I’ve seen many in the pulpit, but I suppose that’s off-topic.

  2. js
    Posted October 24, 2013 at 6:10 am | Permalink

    I have just returned home from my neighbours (who is a vet) having helped out giving an injection to a calf that had around 20 paralysis ticks on it.
    It struck me how powerful the toxin (is it toxin or poison or venom?) must be for ticks that are around 2mm to have an effect on animals that weigh 30kg or more.
    This morning I pulled a tick out of the back of my neck.
    Luckily it was only a bush tick.
    It must have got on me through one of my cats that jumps on my bed every morning.
    Just after I noticed the tick on me and pulled it out, I saw another one on the cat.
    They are quite hard to kill,as just squeezing them doesn’t work.
    You have to squash them with tweezers or using the edge of a fingernail against another fingernail.

    • Buzz
      Posted October 24, 2013 at 6:38 am | Permalink

      Burn them in a match flame. It’s actually remarkable to watch them flailing, then just stop, stone dead.

    • Diane G.
      Posted October 24, 2013 at 3:07 pm | Permalink

      I was unaware of “paralysis ticks.” Have just skimmed the Wikipedia article looking for an evolutionary hypothesis for this phenomenon, with no luck. (Appears to be more of a retained characteristic from a previous evolutionary lifestyle.)

      Most interesting.

      FWIW, I’m currently on doxycycline for the effects of a bite of our (USA) Ixodes genus tick…

  3. Seth
    Posted October 24, 2013 at 6:11 am | Permalink

    Venoms can also be injected via stings not only by bites. Very cool though. Next, tardigrades.

  4. uglicoyote
    Posted October 24, 2013 at 6:17 am | Permalink

    Reblogged this on The Road.

  5. darkwavepunk
    Posted October 24, 2013 at 6:33 am | Permalink

    Any chance that trilobites may have also had venom? Is there any way we could tell from just fossil evidence?

    • Posted October 24, 2013 at 7:18 am | Permalink

      I don’t know, but Venomous Trilobite is just begging to be adopted as the name of a garage band….

      b&

    • Posted October 24, 2013 at 8:44 am | Permalink

      The reconstructions of trilobite mouthparts suggests they were mostly for mashing/chewing. I have not seen them with hypertrophied stabby looking fangs. Trilobites were very diverse, though, so it is worth a look.

  6. John Harshman
    Posted October 24, 2013 at 7:51 am | Permalink

    The phylum Arthropoda contains four major living groups, usually considered subphyla: Hexapoda (insects and a few other groups like springtails), Myriapoda (mostly centipedes and millipedes), Chelicerata (spiders, scorpions, horseshoe crabs, mites, etc.) and Crustacea (crabs, lobsters, barnacles, shrimp, etc.).

    This would be a good place to note that Crustacea is paraphyletic: Hexapoda is included within it. And in fact remipedes are one of the “Crustacean” groups that fall outside the clade of hexapods and most crustaceans.

    • chascpeterson
      Posted October 24, 2013 at 10:34 am | Permalink

      That’s incorrect, I think. It was at this very website that I learned that remipedes are members of the crustacean sister-group to hexapods.

  7. Posted October 24, 2013 at 11:13 pm | Permalink

    Thanks again, WEIT, for posting the most intriguing bits of biology.

  8. Dominic
    Posted October 25, 2013 at 2:23 am | Permalink

    The hairs on their legs to aid swimming remind me of shrimps – an ancestral trait both share or evolving more than once in different crustacea?

  9. marksolock
    Posted October 26, 2013 at 11:54 am | Permalink

    Reblogged this on Mark Solock Blog.


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