A class of sponges whose skeletons are made of siliceous hexactine spicules. These exclusively marine sponges are widely distributed in modern oceans. Their fossil record extends from the late Precambrian to the Recent. The basic spicule type of the class is a triaxial hexactine, in which the three pairs of opposed rays are at right angles to each other and lie along one of the three axes of a cube. Proximal ray ends and axial filaments meet at the center of the cube. These principal spicules and variants of that form make up skeletons of the sponges.