Sponges encompass a vast diversity of asymmetrical shapes, sizes, and even hardnesses (ranging from soft and flexible to rock-hard). The beating flagella of the choanocytes create water currents that flow through the canals and pores in the sponge, bringing in oxygen and particles of food that are consumed. The cells lining the inside of the sponge are called choanocytes(‘collar cells’), which have a ‘tail-like’ flagellum. Spongin is the flexible material that makes up the body wall of the sponge, while spicules are hard, spiny secretions that help to provide a reinforced structure. Having no digestive tract, localized sensory region, or true tissues, they are little more than a cluster of cells supported by a structure of sponginand spicules. Sponges make up the simplest animal group on the planet: phylum Porifera (from the Latin porus ‘pore’ and ferre ‘to bear’).
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