Ultrastructure of ionocytes from osmoregulatory integumental windows of Tachidius discipes and Bryocamptus pygmaeus (Crustacea, Copepoda, Harpacticoida) with remarks on the homology of nonsensory dorsal organs of crustaceans

The ultrastructure of the integumental windows of the polyhaline species Ta chidius discipes (Tachidiidae) and the freshwater inhabitant Bryocamptus py gmaeus (Canthocamptidae) is described. The cuticle as well as the underlyin g cells exhibit fine structural features, which show that these windows are sites of ion exchange. The thick epidermal cells possess apical membrane a mplifications and many mitochondria, which in the case of B. pygmaeus are r amified in a very unusual style. The osmoregulatory function can also be sh own by vital staining with silver nitrate. The integumental windows of both species are not innervated. This is also evidenced by SEM observations. An overview about the distribution of integumental windows within the Harpact icoida is given. The question of the homology of nonsensory embryonic and n on-embryonic dorsal organs is discussed.