STRUCTURE AND FUNCTION OF FRESH-WATER SPONGE EPHYDATIA-FLUVIATILIS L (PORIFERA) .3. CAPTURE OF FOOD, DIGESTION AND DEFECATION

E. fluviatilis ingests particulate and dissolved food substances through the incurrent canal system into the open mesenchymal space. Particulate food, especially bacteria, is caught by the choanocytes of the flagellated chamber which form a filter-like structure, and phagocytozed by choanocytes and amoebocytes. The capacity of lysosomal digestion in the amoebocytes exceeds that of other phagocytotic cells. Both choanocytes and amoebocytes are able to transfer their phagosomes to other food-searching cells. Excrements released into the mesenchymal space are transported through the endopinacocytes into the excurrent canal system. Dissolved proteins are pinocytozed by the choanocytes at the inner face of the collar base and accumulated in food vacuoles. These are exocytozed at the basal side of the choanocytes and in turn endocytozed and digested by amoebocytes. Residual bodies with contents of lamellate structure are defecated in the same way via the endopinacocytes of the excurrent canals.