Sponge spicules. Light micrograph of the spicules from unidentified marine sponges (Porifera). Sponges are primitive multicellular animals. Spicules are the intricate skeletal structures that support the body structure of a sponge. They are made of silica or calcium. The shape of the spicules is often specific to the species of sponge, and can be used as an identification tool. Magnification: unknown.