Glass Sponges (Hexactinellida)

Glass sponges, the hexactinellids, are sponges whose skeleton is made of siliceous spicules with six rays intersecting at right angles, much like a toy jack. They are widely viewed as an early branch within the Porifera because living hexactinellids differ so much from other sponges. Much of their tissue is syncytial, with extensive regions of multinucleate cytoplasm, although some discrete cell types such as archaeocytes do exist. Unlike other sponges they cannot contract, and they have a unique system for rapidly conducting electrical impulses across the body, which lets them react quickly to outside stimuli.