Word porifera is derived from latin, porus means minute holes or tiny opening and ferra means to bear . Hence animal of this phylum bear small holes or pores all over the body . These pores are called ostia . Their bodies are made of groups of cells but the tissue and organs are not present . All the members of this phylum are aquatic mostly marine
The ostia are part of canal system in which water circulates and brings food to the body. The food is digested inside body cell ( intracellular digestion) as well as in the spongeocoel ( extracellular digestion) .
Food of porifera includes phytoplanktons, zooplanktons , protozoans, crustacea and other small organisms but the major part (80%) of the food is comprised of dead decaying organic matter . Sponges are sessile ( stationary) and do not contain any locomotary organ . Their dispersal takes place during asexual reproduction by budding and gemmule formation or by sexual reproduction through the formation of eggs and sperms . Process of excretion takes place by diffusion.
Sponges also lack any nervous system. Neurosensory cells and neurons are found which are believe to coordinate the flow of water .
All sponges except class mykospongida have skeleton . The skeleton consist of carbonate of lime or silicone in the form of spicules or of spongin ( a fibrous protein) in the from of fibers. Sponges are economically important animal as they are used for washing and bathing by human beings from ancient times. Even after the production and availability of artificial sponges , still natural sponges have their demand in the world. Sponges found in the warm waters of mediterranean sea are commercially more important . Sponges are used in surgical operations because of their ability to absorb blood and other fluids . To reduce the noise pollution and to make the buildings sound proof, sponges are used to absorb sound waves . Examples are sycon (a common sponge ) , Euplectella or venus flower basket (a very beautiful, delicate siliceous sponge appear to be made of glass framework) etc.
Predatory sponge have recently been discovered near the lip of a mud volcano in Barbados trench, 5000 meters beneath the sea . They belong to family CLADORHIZIDAE . They are very large, about the size of a large dog. They stab passing crustaceans with their spicules and consume them.