Porifera, sea sponges, are the among the most primitive and multi-cellular Animals, being part of the Animalia Kingdom. Porifera are mainly marine creatures and so far, 5000 different species have been identified. Porifera are sessile, having no stalk and are not locomotive.
They are asymmetrical and have no mouth, no muscles, no digestive or circulatory systems and no nervous system. There are three different classes of sponges; bony (Calcarea), glass (hexactenellida) and spongin (demospongiea). Porifera have pores through their body and an oscula, to excrete waste and they also lack different cell layers. They are composed of 3 different types of cells, Epithelial cells, which cover the inner and outer surface of their body, whose function is to control the pores size, to regulate the flow of water, Collar cells, which have flagellum that beat in the inner canal to maintain the flow of water and filter out micro organisms, and Amoeboid cells, which travel between Epithelial and Collar cells and function is to digest and distribute nutrients, produce reproduction cells and develop the internal skeletons which are composed of spicules formed from calcium carbonate or silica, top support the body. Porifera are hermaphrodites.
They reproduce sexually by releasing their sperm and eggs, which fertilize other sperm and eggs that were released. This is usually done on specific days during the night. They reproduce asexually, by either internal budding, where archaeocytes collect in the mesophyl and become surrounded by spawning, and external reproduction, where a bud grows on the outside of the body, or a part breaks off and grows into a new sponge.
Porifera are filter feeders. They pump water into their spicules and filter out the particles of food makers. As water travels throughout the sponge, it absorbs oxygen and releases waste through gas exchange and filters our small organisms. Respiration and excretion are done by diffusion.
