Any of the many sponges of class Hexactinellida, which have hexactine spicules; a glass sponge.
2007, S. P. Leys, et al., The Biology of Glass Spomges, David W. Sims (series editor), Advances in Marine Biology, Volume 52, page 78,
Spicules of hexactinellids are nearly indistinguishable from those of demosponges in most measured characteristics.