SPONGES
A sponge eats by drawing water through its pores and filtering organic particles. The water is then ejected back into the surrounding environment. The entire surface of the sponge is able to carry out this process, making it an extremely efficient filter feeder. Coral reefs offer abundant supplies of nutrients, making them ideal habitats for sponges. As simple animals, sponges are collections of cells containing no actual tissue or organs.Although adult sponges are fundamentally sessile animals, some marine and freshwater species can move across the sea bed at speeds of 1–4 mm (0.039–0.157 in) per day, as a result of amoeba-like movements of pinacocytes and other cells. A few species can contract their whole bodies, and many can close their oscula and ostia. Juveniles drift or swim freely, while adults are stationary.[4]Sponges in temperate regions live for at most a few years, but some tropical species and perhaps some deep-ocean ones may live for 200 years or more. Some calcified demosponges grow by only 0.2 mm (0.0079 in) per year and, if that rate is constant, specimens 1 m (3.3 ft) wide must be about 5,000 years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old.[4]
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