A neotype of Amphitrite Müller (1771) is established and re-described, using material collected in 2001 from near the type locality on the southwest coast of Iceland. We examined material from Iceland, Nova Scotia and Newfoundland, identified as Pseudopotamilla reniformis, showing scissiparity and commonly found in aggregations within kelp holdfasts or amongst encrusting fauna. By contrast, scissiparity has not been seen in a population recorded as P. reniformis from Wales (broadcast spawning is presumed, Chughtai & Knight-Jones 1988), which bores into limestone and that the present analysis shows to belong to a different species from P. reniformis. Sabella oculata Krøyer (1856, Norway) is a junior synonym of P. reniformis. Sabella aspersa Krøyer (1856, Greenland) and Sabella saxicava (Quatrefages, 1866, France) are re-instated and re-described in Pseudopotamilla. Pseudopotamilla saxicava (= Potamilla ehlersi Gravier, 1906) has a widespread distribution from Britain to the Arabian Gulf, Pseudopotamilla aspersa is found in Greenland and the distribution of P. reniformis is reduced to Iceland, northern Norway, Nova Scotia and Newfoundland. The genera Eudistylia Bush and Schizobranchia Bush are discussed in relation to Pseudopotamilla.
Keywords: Coelenterata, Fan worms, Sabella aspersa, Sabella saxicava, scissiparity, neotype, rock borings.