Key facts

Length up to 8 cm, width up to 2 mm. Dorsal side of body usually bright red and domed, ventral side distinctly paler and somewhat flattened. Head eyeless, somewhat flatter and wider than body, with lateral slits extending backwards to the cross furrow by which the head is demarcated. Upper side of head with a characteristic white patch of varying size and shape (sometimes covering the entire head except the outermost apex). Caudal cirrus small and translucent, often indistinct and frequently lost. Found on shell gravel bottoms, among algae (e.g. Corallina spp.) or cnidarians, sponges (Porifera) etc. on rock, and on sandy clay. First recorded in ERMS region in 2006 (Skagerack).