part of part_of part of develops from develops from sponge cell macromere pinacocyte 2011-04-22T07:11:56Z cjm flat cells found on the outermost layer of sponges. They can expand and contract to slightly alter the size of the sponge, and can also produce collagen. Delimits the sponge from the external milieu and always only in a layer one-cell deep pinacoderm