The array of spines carried by a regular echinoid (eg Echinometra above) offers a formidable defence against predators. The spines can be locked into position by special tissue termed catch apparatus. Although most irregular echinoids avoid predators by living out of sight within the sediment, there are certain marine snails that search out buried urchins and feed on them by drilling through their test. There are therefore also irregular echinoids that possess an armour of long aboral spines to ward off predators.
Deep-sea echinothurioids may have poison sacs associated with their aboral spines to ward off predators.