THE ULTRASTRUCTURE OF IONOCYTES FROM OSMOREGULATORY INTEGUMENTAL WINDOWS OF PARASTENOCARIS-VICESIMA (CRUSTACEA, COPEPODA, HARPACTICOIDA)

Species of Parastenocarididae with a few exceptions have integumental windows on the dorsal side of the cephalothorax and of four (male) or three (female) abdominal somites. By vital staining with silver nitrat e and by ultrastructural observations it can be shown that these windo ws are sites of ion exchange. The cuticle of these windows is very thi n and the epidermal cells underlying it show apical invaginations of t he plasma membrane and abundant mitochondria. The cephalothoracal wind ow could be shown by SEM to consist of two components. A central windo w for osmoregulation is surrounded ring-like by a second one of unknow n function. It is shown for the first time that a species of Chappuisi idae (Harpacticoida), Chappuisius inopinus KIEFER 1938, also has windo ws as revealed by vital staining with silver nitrate. These windows ar e oval and lie dorsally on the thoracal somites bearing the peraeopods 3, 4, and 5 respectively.