Q Elsevier/North-Holland Biomedical Press THE PELAGIC AND BENTHJC PHASES OF POST-METAMORPHIC

Abstr-ct: Some post-melamorphic individuals of Munidit gregaria (Fabricius) are permanent members of the K-nthos while others spend at least part of their time in the water column. These two types of individual are distinct, both morphologically and in the composition of the body. Pelagic specimens have a low density throughout the moult cycle, brought about by a high water content, and low ash and calcium contents. Benthic individuals have this low density for only the first few days post-moult. Normally the pelagic habit is retained only during the first summer as post-larvae but on occasions it is extended over the whole year. In captivity specimens collected at the surface quickly settle on the bottom of the tanks and do not reappear at the surface. The strong positive phototactic response, seen when the animals are collected from the surface, is lost in the first few weeks and the low density persists only until they moult