Spicules are small, needle-like structures found in various organisms, particularly in sponges and corals. In sponges, they provide structural support and can be made of silica or calcium carbonate. These tiny elements help maintain the shape of the sponge and protect it from predators. In addition to sponges, spicules are also present in the anatomy of some echinoderms, like sea urchins. In these creatures, spicules contribute to the overall rigidity of their bodies. The presence of spicules is an important feature that aids in the classification and study of these marine organisms.