The syncytial nature and phagocytic activity of the branchial podocytes in the grass shrimp, Palaemonetes pugio.

The morphology of the branchial podocytes in the grass shrimp, Palaemonetes pugio, was investigated in relation to the molt cycle. The podocytes are located in the efferent hemolymph channels in the gill axis, and possess a specialized plasmalemma consisting of interdigitating pedicel processes which are bridged by thin diaphragms. The topography of the plasmalemmal surface suggests that these cells, like similar cells in other arthropods, function in the ultrafiltration of micro- and macromolecular substances from the hemolymph. Additionally, the branchial podocytes exhibit phagocytic activity. This activity, though evident during the pre-molt period, is most prominent during the early post-molt period. Among the cell types subjected to phagocytosis by podocytes are the secretory cells of the tricellular and rosette-type dermal glands and the epithelial cells of the gill axis. During the late pre-molt and early post-molt periods, the podocytes often appear as syncytia, containing as many as four nuclei. The exact interrelationships between phagocytosis and syncytial formation remain to be ascertained. These aspects and the possible ambulatory abilities of the branchial podocytes are discussed.