Wikipedia:POTD column/June 27, 2006
Prosobranchia are gastropods with gills in front of the heart. The prosobranchs are almost all marine snails, among them conchs, cones, cowries, limpets, murexes, periwinkles, volutes, and whelks. They all have an operculum, a horny plate situated at the foot, by which the snail can close the aperture, when the body is retracted into the shell. Most have spirally coiled shells. Their nervous system has twisted into a figure-8 shape. The eyes are situated on tentacles.