<P> Spicules are structural elements found in most sponges . They provide structural support and deter predators . Large spicules that are visible to the naked eye are referred to as megascleres, while smaller, microscopic ones are termed microscleres . </P> <P> Spicules are found in a range of symmetry types . </P> <P> Monaxons form simple cylinders with pointed ends . The ends of diactinal monaxons are similar, whereas monactinal monaxons have a different ends - one pointed, one rounded . Diactinal monaxons are classified by the nature of their ends: oxea have pointed ends, and strongyles are rounded . Spine - covered oxea and strongyles are termed acanthoxea and acanthostrongyles, respectively . Monactical monaxons always have one pointed end; they are termed styles if the other end is blunt, tylostyles if their blunt end forms a knob; and acanthostyles if they are covered in spines . </P> <P> Triaxons have three axes; in triods, each axis bears a similar ray; in pentacts, the triaxon has five rays, four of which lie in a single plane; and pinnules are pentacts with large spines on the non-planar ray . </P>

Why are spicules used as a primary characteristic in the taxonomy of sponges