What is "hexactinellid"

Hexactinellid \Hex*ac`ti*nel"lid\, a. (Zo["o]l.) Having six-rayed spicules; belonging to the Hexactinellin[ae].

n. Any of many sponges, of the class Hexactinellida, that have hexactine spicules; the glass sponges

Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma.