Venoms are toxins transmitted via some delivery mechanism. Envenomations are poisonings caused by a bite, sting, or puncture. Sea creatures use venoms for killing or stunning prey or as a counterattack against potential predators - or both. Although many sea animals are toxic, only a small proportion of these species can actively deliver their toxins, and are thus considered venomous. The spines of echinoderms, the bristles of fire worms, and the stinging cells of the jellyfish tentacles all lie in wait passively for their victims to swim or drift by.
Injectors are more aggressive.
Octopods and sea snakes bite. The spines and rays of various fishes puncture the skin of their antagonist, and the slow-moving cone snails thrust their fatal darts at overly curious creatures. C oelenterates, the group of marine animals that people most often encounter, best exemplify passive means for delivering venom. Of the 9,000 species worldwide, about 100 coelenterates are toxic to humans, though only a few can be fatal. Their bodies take the form of either a free-swimming medusa or a sessile polyp, but each form has a ring of tentacles surrounding a central mouth.