A detailed description is given of the anatomy of the head, thorax, proboscis apparatus and pygidium of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparède) (=Caesicirrus neglectus Arwidsson, 1911). The head consists of prostomium, peristomial region and one achaetous segment which is undoubtedly a metamere. Whether the peristomium should be counted as another rests on the definition of a metamere, about which opinions differ. Evidence is presented which suggests that each of the two paired groups of proboscideal retractors is derived from a head septum.

Probably because of the relatively large size of the proboscis, not only the head, but also the first four chaetigers (= thorax) act as a pump to effect the eversion of the proboscis by coelomic fluid pressure. The thoracic septa are highly specialized in relation to this function. In both gross and detailed anatomy, and in mode of functioning of the region, the maldanids show many resemblances to some arenicolids.

The pygidium consists of a ring-shaped thickening (the callus ring), the anal funnel and the anal cone.

Based on this investigation of anatomy, a system of description is suggested which aims to avoid ambiguity and to eliminate from future maldanid literature the type of confusion which exists in it at present.