The body is soft, very slender, and elongate. Along each side of the mantle edge is a wavy ridge upon which are situated short, pointed cerata. These cerata lack gills, and in fact gills or secondary gill structures are entirely absent in this family. The rhinophores have transverse lamellae on the club with a blunt knob rising at the distal end. There are tall sheaths surrounding the rhinophores and these sheaths bear papillae around the lip. They have one or two pairs of oral tentacles but no developed oral veil. The anterior corners of the foot are tentacular or simply rounded. All species feed upon hydroids and are cryptic in situ.