Figure 1.  Anatomy of a generalized, solitary ascidian.  Redrawn from Barnes 1980. 

Ascideans, also called sea squirts, are sessile filter feeders that include both solitary and colonial types.  As members of the phylum Chordata, they are grouped with both vertebrates and the lancelets, and are united with these morphologically different groups by the presence of a notochord (a dorsally placed rigid rod), gills slits, and a dorsal hollow nerve cord. 

Ascideans utilize 2 siphons to draw water through their bodies.  The buccal siphon draws water and tiny food particles into the body where food is filtered against the pharyngeal basket and passed to the esophagus for digestion.  Filtered water, body wastes, eggs and sperm, and in some species larvae, all exit the body by way of the atrial siphon.