(class Gastropoda, subclass Opisthobranchia)
An order of molluscs in which individuals are very small and benthic, living between sand grains. The visceral sac is thin and spiculate, and is often much longer than the foot and markedly separate from it. There is no shell. These gastropods are deposit feeders. According to different authorities the order contains three families or only one.
Subjects: Zoology and Animal Sciences.