The structure, ultrastructure and osmoregulatory function of the branchial chamber were investigated in Palaemon elegans (Rathke, 1837) by light microscope, electron microscope and immunohistochemistry methods, respectively. Each chamber possesses a branchiostegite, 3 epipodites and 8 phyllobranchiate gills. The lamellae are attached along the two outer surfaces of the triangular gill axis. Ultrastructurally, numerous ionocytes are present along the innerside of the branchiostegites and in the epipodites. A consistently high immunofluorescence of Na+, K+-ATPase was observed along the basolateral sides of these ionocytes. The gill lamellae are formed by a single axial epithelium made of H-shaped cells with thin lateral expansions and a basal lamina limiting hemolymph lacunae. A positive but weak fluorescence of the Na+, K+-ATPase was found in lacunae sides of the lamellae cells. These findings show that in P. elegans, the epipodites and the branchiostegites organs appear as the main site of osmoregulation and the gill lamellae are mainly devoted to respiration
