Nutrition: Their food consists of bacteria, microscopic algae, protists and other suspended organic matter. Preys are slowly drawn into the sponge and digested. Large population of sponges play an important role in reducing the pollution of coastal waters. A single leucon with size 1cm in diameter and 10cm high can filter 20 liters of water everyday. A few species are carnivores. The deep water Asbestopluma have spicules covered with filaments and captures small crustaceans with the help of these spicules. Mechanism of feeding: Choanocytes filters small suspended food particles. Water passes through their collar near the base of cell and then moves out from choanocytes into the sponge chamber through the open end of collar. Suspended food is trapped on the collar. It passes through microvilli and reaches at the base of the collar. It forms a food vacuole in collar and the PH of food is changed. Digestion in food vacuole takes place by lysosomal enzymes and partially digested food is passed into amoeboid cells. Amoeboid cells distribute it to other cells. Pinacocytes lines the incurrent canal and large food particles can enter into pinacocytes by phagocytosis. Sponges also absorb nutrients dissolved in seawater by active transport.
Excretion and respiration: There is extensive canal system in sponges and a large volume of water circulates through these canals. All cells are in close contact with water. Thus, nitrogenous waste(ammonia) is removed and gas exchange occurs by diffusion. Waste products diffuse out of cells into the surrounding water. Choanocytes help to remove waste and excess water. Oxygen diffuses into cells from surrounding water. Oxygen rich water circulates through canals and chambers. Choanocytes also facilitate oxygen uptake.
Coordination: Sponges do not have nerve cells to coordinate by functions and mostly individual cells show response to a stimulus. For example, light inhibits the constriction of cells surrounding the ostia. It keeps the incurrent canals open. Therefore, water circulation through some sponges is minimum at sunrise but it is maximum just before sunset. Some other reactions suggest that some communication is present among cells. For example, the rate of water circulation through a sponge can drop suddenly without external cause. This reaction takes place due to choanocytes. It stops the activities simultaneously. These reaction shows that some form of internal communication is present in them. The nature of this communication is unknown. Amoeboid cells may transmit chemical messages and ion movement over cell surfaces. It is possible control mechanism.
Reproduction:
Sexual reproduction: Most sponges are monoecious but they produce eggs and sperms at different times. Therefore, they do not self fertilized. Certain choanocytes lose their collars and flagella. They undergo meiosis and form flagellated sperm. Other choanocytes(and amoeboid cells in some sponges) undergo meiosis and form eggs. Eggs are retained in the mesohyl of the parent. Sperm cells passes from one sponge through the osculum and enter another sponge with the incurrent water. Sperms are trapped by choanocytes. Sperm is covered into a vacuole in choanocytes. Choanocytes lose their collar and flagellum and become amoeboid cells. It transport sperms into the eggs and zygote is formed. Early development occurs in mesohyl and cleavage occurs in zygote. A flagellated larval stage is formed. These larvae may be parenchymula larva or amphiblastula larva. The larva becomes free and water currents carry the larva out of the parent sponge. It freely swims for two days. Then larva settles on substrate and develops into the adult body form.
Asexual reproduction: Asexual reproduction takes place by gemmule formation. Gemmule is a resistant capsule containing masses of amoeboid cells. The parent sponge dies in winter and it releases gemmules and gemmules can survive both in freezing and drying condition. The condition become favorable in spring. Now the amoeboid cells come out through tiny opening called micropyle. It develops into a sponge. Some sponges posses great powers of regeneration. Portion of them are cut or broken and the broken piece forms new sponge.
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