hexactine

from The Century Dictionary.

• noun In the nomenclature of the spicular elements of sponges, a six-rayed or triaxial form typically expressed as six arms at right angles to one another.
• Having six rays: same as hexactinal.
• Having the characters of or pertaining to a hexactine.
• Hexactinellidan.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Having six rays
• noun A six-rayed spicule, made of silica, that makes up the skeleton of some sponges