Pinacocyte
Pinacocytes are part of the epithelium in sponges. They play a role in movement (contracting and stretching), cell adhesion, signaling, phagocytosis, and polarity. Pinacocytes are filled with mesohyl which is a gel like substance that helps maintain the shape and structure of the sponge. These are the cells in contact with the sponge's substrate (the surface to which it is attached). These are found on the exterior of the sponge. Exopinococytes produce spicules which is a needle like process that serves as structure for the organism. These line the sponge's interior canals.
Function
Pinacocytes are not specific to the sponge however.