Each cell of a sponge is responsible for its own nutrition. There are three main cell types in a sponge. The epithelial cells are on the surface. Collar cells or choanocytes are the work horses. They are responsible for filtering all of the food and waste.
Amoeboid cells produce the skeletal elements known as spicules.
Some sponges have spicules that are made of flexible protein called spongin. From this type of sponge, bath sponges are produced. Reproduction in sponges is either sexual or asexual. Sometimes planktonic sperm is filtered in creating sexual reproduction. Sponges are marine creatures that can be found in almost all habitats including polar regions.