Phylum Porifera includes the most primitive and simplest animals. They are commonly called sponges.
(a)They show cellular level of organisation. The cells are almost independent,cooperating very little with one in their function.
(b) The sponges are diploblastic i.e., the sponges develop from two germs layers called ectoderm and endoderm.
(c) The sponges have porous body viz. provided with pores. The pores are of two types : inhalent pores are called ostia (e.g. ostium) and exhalent pores are known as oscula (e.g. osculum).
(d) The animals possess a large cavity called spongocoel. It opens to the outside by a terminal opening called osculum.
(e) One of the most important features of sponges is the presence of an interconnected network of channels called canal system. Water enters the spongocoel through ostia and goes outside through osculum.
(f) The sponges possess an internal skeleton of calcareous or silidous spicules or irregular proteinaceous spongin fibers or both located in mesenchyme.
(g) Sponges reproduce both asexually and sexually.Asexual reproduction occurs by budding or special cell mass called gemmules or internal buds. Sexual reproduction involves the formation of ova and spermatozoa.