Experts have found the first venomous crustacean - a centipede-like creature that lives in underwater caves.
The blind "remipede" liquefies its prey with a compound similar to that found in a rattlesnake's fangs.
It lives in underwater caves of the Caribbean, Canary Islands and Western Australia, feeding on other crustaceans.
The venom contains a complex cocktail of toxins, including enzymes and a paralysing agent.
The findings are detailed in the journal Molecular Biology and Evolution.
The remipede (Speleonectes tulumensis) breaks down body tissues with its venom and then sucks out a liquid meal from its prey's exoskeleton.
Co-author Dr Ronald Jenner, a zoologist at London's Natural History Museum said: "The unique insights from this study really help improve our understanding of the evolution of animal venoms.
"The spider-like feeding technique of the remipede is unique among crustaceans. This venom is clearly a great adaptation for these blind cave-dwellers that live in nutrient-poor underwater caves."
Crustaceans are a large group of the wider category of animals known as arthropods. They include shrimp, krill, lobsters and crabs.
Most are aquatic, but a few - such as woodlice - live on land.
Dr Bjoern von Reumont, also from the Natural History Museum commented: "This is the first time we have seen venom being used in crustaceans and the study adds a new major animal group to the roster of known venomous animals.
"Venoms are especially common in three of the four major groups of arthropods, such as insects. Crustaceans, however, are a glaring exception to the rule.
"While they can be as varied as tiny waterfleas, krill, crabs and barnacles, not one of the approximately 70,000 described species of crustaceans was known, until now, to be venomous."