The nature and role of the basal pinacoderm in the freshwater sponge Corvomeyenia carolinensis Harrison was examined using phase contrast microscopy, cytochemistry, and morphogenic analysis of regeneration. The pinacoderm is a nonsyncytial simple squamous epithelium. Pinacocytes, normally nucleolate, contain little histochemically demonstrable RNA, suggesting low levels of protein synthesis. The lack of a major role in food storage is indicated by the slight amount of PAS-positive carbohydrate and the absence of glycogen and acid mucopolysaccharides. Marginal pinacocytes are active in feeding. High levels of acid phosphatase in these cells indicate digestion is following ingestion. Pinacocytes contain numerous contractile vacuoles and play an active role in osmoregulation. These cells play the dominant role in wound healing, becoming actively ameboid to initiate the regenerative process.