A morphological study on posterior gills of the mangrove crab Ucides cordatus

Morphological and histological studies on posterior gills of the mangrove c rab Ucides cordatus showed that the 5th gill (of 7) has a larger surface ar ea and a greater number of lamellae compared to the 6th gill. Regular separ ation of gill lamellae, important when the gill is in air, is maintained by enlargements of the marginal canals. Conical, spine-like structures along the efferent vessel of both 5th and 6th gills were also observed. In additi on, pillar cells, a discontinuous lamellar septum and a hypobranchial arter y were observed, The presence of valvelike structures near the efferent ves sel was also indicated. These structures, together with the pillar cells, m ay have a role in directing the hemolymph flow towards certain gills during particular physiological states. Localization of osmoregulatory epithelia in the lamellae of both gills was inferred from dimethylaminostyrylethylpyr idiniumiodine staining. Apparently gills 5 and 6 have osmoregulatory epithe lial cell patches of similar area, corresponding to 43% and 38% of the tota l lamellae area, respectively. However, their localization is quite differe nt. Gill number 5 osmoregulatory patches seem to be restricted to the affer ent region of the lamella whereas in gill number 6, they are more dispersed over the entire lamella, These differences may be related to the particula r functional characteristics of these gills.