a1 Department of Zoology, Queen Mary College, University of London
Lasaea rubra, like other small Erycinacea, is unusual among eulamellibranchs in its relatively great mobility on the surface of the substrate. It can crawl about as freely as a small gastropod and lays down a mucous trail for the attachment of its progressing foot, drawing the shell and body rhythmically forward after each advance thrust of the foot. Unlike some other Erycinacea, L. rubra has no well-defined sole; it attaches by the sharp lower edge and part of the side of the foot, which is strongly ciliated and well supplied with mucous glands. In most burrowing eulamellibranchs, the site of communication with the surrounding water has shifted to the paired siphons at the posterior end. The Erycinacea, however, have an anterior inhalant siphon; and—as in forward moving prosobranch gastropods (Morton, 1958)—there is an obvious adaptive advantage in receiving the ingoing current from the water into which the animal is moving.