Cuvier, 1804
Internal shell approximately one half the body-length (in North Sea representatives).
The mantle bears retractile conical tubercles; the rim is often emarginate posteriorly in life to form an exhalant respiratory siphon (indetectable after death). The gill bears on the rachis a double row of tubercles; the male opening, anterior to the gill on the right side of the body, is surrounded by a non-retractile external sheath.
The foot may be used for creeping or, by expansion of its lateral areas, employed in swimming; the two halves of the foot beat alternately during natation.
The radula of British material contains some teeth which bear an extra sub-terminal spine. The jaw elements each bear three stout denticulations.
Source: Thompson, 1988.
The following species occurs in the region:
Pleurobranchus membranaceus