Psolus

Jäger, 1833

53 species

Tentacles 10. Tube feet developed almost exclusively on the ventral sole. Outside the sole, tube feet are found only on the soft skinned introvert, and there in the shape of small papillae around the anal opening. The whole dorsal side is covered with thick, mostly imbricating scales, which usually carry small rounded grains on their surface. In the ventral sole, only scattered microscopical plates are found. (Mortensen, 1927)

Distinct sole on ventral surface. Tube feet absent from dorsal surface except for a few sensory tube feet on introvert and around anus. Tentacles 10, all of even size. Dorsal surface covered with thick, imbricating plates, but ventral surface has only a few scattered ossicles in the body wall. (McKenzie, 1991)