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The Class Ophiuroidea ("snake-tail form"), which contains forms known as brittle stars and basket stars, is the largest and most successful group of echinoderms. The animals are called brittle stars because their arms (which are long and slender) break off easily when seized by a predator, but are easily regenerated. The animals are quite mobile, moving with a writhing, serpent-like motion in search of prey and particulate matter that they collect with their arms and tube feet. The mouth is equipped with five moveable plates bearing teeth formed from modified spines that serve as jaws. There is a sac-like stomach in the central disc but no intestine or anus! Gas exchange in ophiuroids takes place in five pairs of membranous pouches called bursae that branch off the oral disc. Eggs may be fertilized externally or sometimes within the bursae, which can serve as brood chambers.
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