part of part_of part of produced by produced by mesohyl sclerocyte spicule 2011-04-22T06:59:28Z A component of the mineral skeleton, typically composed of silica or calcium carbonate[portol]. A structural element that provides structural support and deter predators. Large spicules, visible to the naked eye are referred to as megascleres, while smaller, microscopic ones are termed microscleres. The meshing of many spicules serves as the sponge's skeleton. Spicules are formed by sclerocytes, which are derived from archaeocytes. The sclerocyte begins with an organic filament, and adds silica to it. Spicules are generally elongated at a rate of 1-10 μm per hour. Once the spicule reaches a certain length it protrudes from the sclerocyte cell body, but remains within the cell's membrane. On occasion, sclerocytes may begin a second spicule while the first is still in progress. cjm located primarily in the mesohyl, but some project through the pinacoderm (Barnes). siliceous or calcareous entities that form the mineral skeleton of a sponge mineral skeleton acellular anatomical structure