Hexactinellid sponges, commonly referred to as glass sponges, are those sponges with a silaceous skeleton made of four- and/or six-pointed spicules. They are distributed worldwide, usually at depths between 200 and 1000 m, and are especially abundant in the Antarctic. All glass sponges are upright, and have specialized structures at their bases for securing themselves to the ocean floor. Typically they are cylindrical, but may also be cup-shaped, urn-shaped, or branching. The average height of a hexactinellid is between 10 and 30 cm.
Because there are several very important, fundamental differences between hexactinellids and other sponges, many experts now suggest that Hexactinellida comprises a distinct phylum.