What are sponges?

Sponges are very primitive many-called animals. They live in both fresh and sea water and encrust rocks and underwater objects in strange lumpy masses. Some spread over considerable areas, others hang in finger-like clusters, while others stand erect, branching irregularly up to 5 feet in height. Sponges are interesting because they represent a more advanced stage of development that the colony of protozoans. They belong to the rhythm Porifera. An individual sponge has a definite vase-like shape, and group of the cells of which it is made are adapted to carry out special tasks. The cells of the wall of the sponge are called ‘covering cells’, and these protect it and help keep its shape. The inside layer of cells consists of cells bearing a whip-like flagellum to lash the water and make current, as well as other cells which form pores on the outside of the sponge. Between the two, amoeba-like cells occur and these secrete strengthening rods called ‘spicules’ which make the sponge rigid.