If you wanted to find a venomous animal, you could do far worse than picking up a random arthropod—the group of animals that includes spiders, scorpions, centipedes, ants, bees and wasps. The group includes hundreds of thousands of venomous members, who inject their debilitating chemical weapons via fangs and stings.

Within this toxic dynasty, one of the major arthropod groups—the crustaceans—sticks out. There’s no such thing as a venomous crab or lobster, prawn or shrimp. There are some 70,000 species of crustaceans and, until recently, it seemed that all of them were venom-free.

The only exceptions live in coastal caves, which are connected to the ocean by underground tunnels. The dark, salty worlds are home to blind, white, sinuous creatures called