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Friday, September 05, 2014

A Venom First: Toxin-Spewing Crustacean

Photo of the poisonous remipede, a living fossil nearly unchanged for 300 million years.
Researchers report discovery of the first venomous crustacean, a remipede much like this one, which lives in submerged caves in Mexico and Central America. Photograph by Wes C. Skiles, National Geographic.
No longer than your pinky and totally blind, the cave-dwelling Speleonectes tulumensis is still one bad-arsed little sea creature—and now the first of some 70,000 crustacean species to be confirmed as venomous.
As reported in the journal Molecular Biology and EvolutionS. tulumensis deploys a nasty chemical cocktail that includes a paralyzing neurotoxin and enzymes that quickly break flesh down into a digestible slurry.
In short, it turns its prey of shrimp and small fish into milkshakes. (Related: “On the Origin of Venom.”)
The S. tulumensis is a wiggly, white crustacean—long and leggy like a centipede—and the largest of its group, the remipedes.
As reported by biologists Bj√∂rn von Reumont and Ronald Jenner, both of the Natural History Museum in London, and colleagues from Germany and Mexico, venomous species—such as spiders, scorpions, ants, bees, and centipedes—are common in three of the four main groups of arthropods, but until now crustaceans appeared to be venom free.
Toxic Shock
When S. tulumensis was first described in 1987—the remipede group having been discovered in ’79—its needle-like fangs suggested it might be equipped to inject venom. Another potential clue: Scientists reported seeing remipedes in the wild discarding empty shrimp shells, presumably after feasting on the insides. But no one knew for sure they were using venom.
It makes sense they’d evolve this survival strategy, says von Reumont. Unlike, say, a mantis shrimp that uses its size and brute force to capture its food, “remipedes are small, fragile, and live in dark underwater cave systems. So they need a good efficient trick to catch—and then not lose—their prey.” Venom is the trick evolution provided.
And not just any venom. “Our molecular study revealed a surprisingly highly adapted venom with a complex composition and a highly developed delivery apparatus,” von Reumont says. In other words, both the animal’s toxic spit and its biting parts were impressive.
Mysteriously, this remipede’s venom recipe resembles that of rattlesnakes more than it resembles that of more closely related arthropods—a great example of convergence (when a trait arises independently in unrelated animals).
A final surprising finding: Its neurotoxin is unique to S. tulumensis. “It’s the ingredient that instantly overwhelms the prey,” von Reumont says, which is key to keeping a blind predator from going hungry.
Risky Business
It’s not easy to study remipedes in the wild; they reside in labyrinthine marine-cave networks in Mexico and Central America that even experienced divers may think twice about entering.
Cave diving for crustaceans isn’t for everyone, concedes von Reumont. “It is quite tough training, and you need to be mentally and physically stable, and should not be stressed too easily,” he says. “Oh, and you must not be afraid of the dark or of diving without a mask and fins.” Because of the tight squeeze in cave tunnels, not everyone can have his or her own air tank: “You breathe in a share of air from your buddy while diving out blind [like a remipede!] along the guideline to the cave’s exit.”
Sounds … insane.
But it’s worth it, apparently. Now von Reumont and colleagues can tell their friends that not three, but all four arthropod groups have venomous members. And for biologists, that’s big news hidden in a very small, deadly package.
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