pinacoderm

The pinacoderm is the outer layer of cells that covers the surface of a sponge and lines its internal waterways. This simple epithelium is composed of flattened cells called pinacocytes. These cells are capable of contracting, which can reduce the sponge's overall volume if it is disturbed. In some sponges, specialized pinacocytes called porocytes form pores that allow water to enter the sponge, and these can contract to close the pores when necessary. The pinacoderm plays a role in the sponge's form and function, although sponges lack true organs.12