In sponge anatomy, one of the spicules forming six equal and similar rays meeting at right angles: Mr. Smart, the biology teacher, showed the students in his class a big photo of a skeleton of a sponge showing the triaxial form of its hexactines exemplified by its six arms grouped at right angles to one another.

A "spicule" is a small pointed structure serving as a skeletal element in various marine and freshwater invertebrates, such as sponges and corals.