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:

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:

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:

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

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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.