Ascidiacea (class)

Scope note: Class of sac-like marine filter feeders characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are much less robust. They have with some primitive vertebrate features, found in all seas from the intertidal zone to the greatest depths. The tadpole-like larvae are free-swimming and have a notochord (a flexible, rod-like structure common to all vertebrates) and a nerve cord in the tail. When the larva finds a place to settle, it attaches itself with a sucker; the tail with its notochord and nerve cord is absorbed and disappears. They are commonly found on pier pilings, ships' hulls, rocks, large seashells, and the backs of large crabs. Some species live individually; others live in groups or colonies. Adults have functional male and female reproductive organs; fertilization occurs when eggs are shed into the water and come into contact with sperm from another individual.

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