"beaten and scraped to rid the skeletons of the dead tissue"

"Sponge, a simple, aquatic animal that looks like a plant. The term is also used for the skeleton of certain types of these animals; the skeleton soaks up fluid easily."
"Sponges do not have heads, arms, or internal organs."
"They have the remarkable ability to restore lost parts, and a new sponge can grow from a small cutting removed from another sponge."
"The surface contains numerous small entrance pores, called ostia, and larger exit holes, called oscula. The canals provide shelter for thousands of small aquatic animals that live there, either permanently or temporarily.The canals are lined with whiplike cells called choanocytes, the movements of which create currents that cause water to flow through the canals. In passing through the sponge, the water gives up oxygen and food and carries away waste products."
thanks to howstuffworks