Animated coloured scanning electron micrograph (SEM) of a fossilised marine sponge spicule from Oamaru, New Zealand. 3-D star shape. Sponge spicules are found in most sponges. They act as the structural support of sponges and deter predators. Spicules can be found in a wide range of symmetry types. They can be made of calcium carbonate, silica dioxide or spongin. Spicules are formed by sclerocytes, which are derived from archaeocytes. There are 4 main types of spicules: monaxons, triaxons, tetraxons and dendroclones.