Sponge spicule

Six-pointed triaxonal siliceous spicule
from a glass sponge

Venus flower basket constructed from
similar spicules

Spicules are structural elements found in most sponges. The meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators.^[1]

Sponge spicules are made of calcium carbonate or silica. Large spicules visible to the naked eye are referred to as megascleres or macroscleres, while smaller, microscopic ones are termed microscleres. The composition, size, and shape of spicules are major characters in sponge systematics and taxonomy.

^ Jones, Adam C.; Blum, James E.; Pawlik, Joseph R. (2005-08-08). "Testing for defensive synergy in Caribbean sponges: Bad taste or glass spicules?". Journal of Experimental Marine Biology and Ecology. 322 (1): 67–81. doi:10.1016/j.jembe.2005.02.009. ISSN 0022-0981. S2CID 85614908.

[1] Jones, Adam C.; Blum, James E.; Pawlik, Joseph R. (2005-08-08). "Testing for defensive synergy in Caribbean sponges: Bad taste or glass spicules?". Journal of Experimental Marine Biology and Ecology. 322 (1): 67–81. doi:10.1016/j.jembe.2005.02.009. ISSN 0022-0981. S2CID 85614908.

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