Spicule (biology)

See also: Spicule

The word spicule is a generic term which gathers extracellular mineral secretions which are present in fabrics of various groups of invertebrates. They can be formed by crystals of Silice, Calcite, or be made of Chitine.

• At the sponges (Porifera), the spicules can be made of calcite (class of the Calcarea) or of silica (class of the Demospongiae, and the Hexactinellida). The siliceous sponges generally have two types of spicules: mégasclères and microsclères. The mégasclères measure more than 100 µm, they take part in the function of support of fabrics. At certain species, the mégasclères can be visible with the naked eye. Among Hexactinellida, certain species are characterized by spicules of very big size which are used as anchoring in the mud. The microsclères are of small size (1 to 100 μm)

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