Sea urchin
Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to . Their tests (hard shells) are round and spiny, typically from across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Pedicellaria
Four main forms of pedicellariae are found in sea urchins : tridactylous, ophicephalous, triphyllous and globiferous. There are typically three valves that make up the jaw of sea urchin pedicellaria. The stalk is composed of a skeletal rod and a flexible neck portion.
They are generally attached by a long, inflexible stalk and may be found anywhere on the sea urchin's test.
In some families, globigerous pedicellariae have evolved into venomous structures, used for protection or maybe hunting. This is particularly the case in the family Toxopneustidae, some species such as "Tripneustes gratilla" and especially "Toxopneustes pileolus" being extremely venomous.