The coelomocytes of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparède) (=Caesicirrus neglectus Arwidsson, 1911) appear to be budded off from particular areas of the somatic peritoneum which overlie large blood capillaries in the thorax and trunk, and from more extensive areas of peritoneum at the posterior end of each tail segment. Both species have large numbers of phagocytic coelomocytes which are similar in structure and behaviour to those of some other polychaetes, and appear to have functions both of excretion and nutrition, and to play some part in regeneration. They have a tremendous capacity for ingestion which is shown particularly in late autumn, when they ingest and digest large numbers of disintegrating gametocytes, and after breeding, when they deal similarly with unshed gametes and debris.

Clymenella has a second type of coelomocyte which is not phagocytic. This type may contain haemoglobin, but the evidence is not conclusive.