* Cells are arranged in a gelatinous non-cellular matrix called mesohyl.īody types: Sponges have three body types: asconoid, syconoid, and leuconoid.Īsconoid sponges are tubular with a central shaft called the spongocoel. * Spicules are stiffened rods or spikes made of calcium carbonate or silica which are used for structure and defense. * Spongocytes secrete spongin, collagen-like fibers which make up the mesohyl. * Sclerocytes secrete calcareous or siliceous spicules which reside in the mesohyl. They also have a role in nutrient transport and sexual reproduction. * Archaeocytes (or amoebocytes) have many functions they are totipotent cells which can transform into sclerocytes, spongocytes, or collencytes. * Myocytes are modified pinacocytes which control the size of the osculum and pore openings and thus the water flow. This is the closest approach to true tissue in sponges. * Pinacocytes which form the pinacoderm, the outer epidermal layer of cells. * Porocytes are tubular cells that make up the pores into the sponge body through the mesohyl. The beating of the choanocytes’ flagella creates the sponge’s water current. The collars are composed of microvilli and are used to filter particles out of the water. * Choanocytes (also known as "collar cells"), flagellated cells which function as the sponge's digestive system, are remarkably similar to the protistan choanoflagellates. Their similarity to colonial choanoflagellates shows the probable evolutionary jump from unicellular to multicellular organisms. With no true tissues (parazoa), they lack muscles, nerves, and internal organs. Sponges are among the simplest of animals. They are primitive, sessile, mostly marine, water dwelling filter feeders that pump water through their bodies to filter out particles of food matter. The sponges or poriferans (from the Greek poros "pore" and ferro "to bear") are animals of the phylum Porifera.
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