Spicules are structural elements found in most sponges, and they are the "bricks" of sponge architecture. The meshing of many spicules serves as the sponges skeleton, providing structural support and potentially defense against predators. Sponge spicules are made of either calcium carbonate or silica, and their composition, size, and shape are major characters in sponge systematics and taxonomy. Large spicules visible to the naked eye are referred to as megascleres or macroscleres, while smaller, microscopic ones are termed microscleres. The morphologies of spicules and their arrangement, together with other important sponge features, such as the shape, consistency, and color, are essential when identifying sponges. Spicules can be of crucial importance for reconstructions of extinct or cryptic sponge communities, and they have been investigated especially with respect to their taxonomic significance.