What Animal Is It?

A remipede
Image Source: Joris van der Ham

For a long time, it was believed that there were no venomous crustaceans in the world. Venom is common in many arthropods, including spiders, scorpions, centipedes and wasps, but of the approximately 70,000 species of crustacean, none were known to be venomous. Until, that is, a species of remipede called Xibalbanus tulumensis – the focus of today’s What Animal Is It? – was studied more closely. But first things first – what is a remipede?

Remipedes are small, pale, blind crustaceans that somewhat resemble aquatic centipedes. They swim on their backs, paddling their many legs; in fact, their name comes from the Latin for ‘oar-footed’. No one knew that remipedes existed until 1979, when they were encountered in a marine cave in the Bahamas. Since then, several more species have been described, all of them in similarly pitch-black submerged caves. Observing these tiny creatures in their natural habitat is understandably difficult because the flooded labyrinths in which they live are hard and dangerous for divers to navigate, so even today they remain mysterious and little-studied.

Nonetheless, new information regarding remipedes has come to light since their initial discovery. In 2007, it was found that Xibalbanus tulumensis kills prey such as brine shrimp by injecting them with venom from its specialised front claws, which resemble hypodermic needles. This venom is a nasty chemical cocktail. It includes a paralysing neurotoxin and digestive enzymes that quickly break the prey’s body tissues down into a liquid slurry. Then the remipede sucks its liquified meal from its prey’s exoskeleton in a similar fashion to spiders, leaving just an empty husk behind. It is suspected that all remipede species are venomous in this way.

A remipede
Despite being just a few centimetres in length, some remipedes have been named after famous giant monsters, such as Godzillius robustus (after Godzilla, of course) and Pleomothra fragilis (after Mothra, Godzilla’s enemy).

Why should remipedes, uniquely among the world’s crustaceans, have developed venom? The answer is probably due to the fact that remipedes are small, fragile, and live in dark underwater cave systems. Prey is scarce and hard to find, so if a remipede does come across a meal, it needs to make sure it can incapacitate it very quickly. Venom is the trick that evolution has provided.  

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