As a rule, the wall of the ovary is continued into a uterine tube opening into the cloaca; but in Philodinaceae this is absent, and the young are free in the body cavity and escape by perforating the cloacal walls.
Un like the molluscs and annelids, however, the cloacal invagination lies outside this region, and the foot is formed by an elongation of the end of the body between the two apertures.
Slender, tapering behind, with subventral cloacal orifice; thin cuticle without papillae; flattened spicules; no gills.
Short, truncate in front and behind; cloacal orifice transverse; gills present; rather thin cuticle; no radula.
The other pair lies just within the lips of the cloacal opening.