The sponges are organisms that do not contain tissues or organs. They live in colonies. However, each cell is responsible for obtaining its own nutrition.
Sponges have three cell types.
The surface cells which are called epithelial cells. Collar cells are flagellated cells that provide current through the pores, and amoeboid cells swim independently. Members of this phylum have cnidocytes, or stinging cells, and nematocysts. Nematocysts are harpoon like structure that is strong enough to penetrate a crab shell. Polyps are fixed with their arms up and medusae are mobile with their arms down.