Pinacocyte

Pinacocytes are flat cells found on the outermost layer (Pinacoderm) of a sponge (phylum Porifera).

Pinacocytes are flattened cells containing many granules; capable of contracting. They are involved in the maintenance of the size and structure of sponge. They can expand and contract to slightly alter the size of the sponge, and can also produce.

Following are the types of pinacocytes:

http://www.encyclopedia.com/doc/1O8-pinacocyte.html

http://www.biology-online.org/dictionary/Pinacocyte

...
Wikipedia