Shell thin to moderately solid, variously sculptured or smooth, aperture shallowly chan¬nelled anteriorly and posteriorly, peristome typically reflected, outer lip often with varix. Operculum thin, simple, nucleus concentric. Radula usually finely cuspate. Animal with long, ciliated cephalic tentacles. Foot typically divided into anterior and posterior portions, but may be simple; with anterior, sole, and posterior mucous glands; tubules of the later extending into the head. Snout moderately long, mobile. Ciliated, elongate caudal and pallial tentacles often present. Penis of male long, straight, closed, not much tapered, usually bearing a narrow terminal filament, attached behind right eye; prostate closed. Female genital tract rather simple, one aperture, pallial duct with a ventral channel. Alimentary canal with jaws, no oesophageal glands, small stomach with large style sac containing a crystalline style. Fine detritus feeders and algal grazers.