Prostomium with two ciliary rings, each with a mid-dorsal interruption. Second ring especially wide, encircling the prostomium at its greatest diameter. Anterior part of the prostomium with four large and several small bristle-like groups of stiff adjoined sensory cilia; with additional single cilia. Ventral side of trunk completely covered with a dense mat of cilia from which two transverse rings per segment run to dorsum. Trunk rings 1-9 dorsally uninterrupted, consisting of individual tufts, which may be distinctly separated from each other. Rings 10 and 11 only in form of lateral transverse rows; small tufts at the level of the anus may belong to a reduced 12th ring. An indistinctly bordered ciliated pit laterally on each side between prostomium and trunk. Two eyes. Caudal appendage, ventral, prominent, extending beyond anus as a bluntly pointed lobe with ventral ciliation and numerous sensory cilia.
Males and females similar: Females with two pairs of ovaries. Mucous cocoon with up to 16 eggs. Males with one pair of testes which may fuse across the mid-line and then occupy most of the body cavity; one pair of ovoid vesiculae; unpaired copulatory organ.
Up to 2.5 mm for 5 segments, if the two rings of the buccal region are considered to be on segment 1.
Sheltered tide pools rich in diatoms, Enteromorpha spp. and Ulva lactuca.
North Sea, English Channel, Irish Sea, Atlantic, Spanish coast, Baltic (Bay of Kiel), Skagerrak, White sea, Barents Sea.