An order of sponges of the subclass Hexasterophora in the class Hexactinellida. The parenchymal mega-scleres in this order are united to form a rigid framework and consist wholly of simple hexactins which are arranged in parallel linear series. The members of each series are united one to another by a secondary envelope of silica. Examples include Hexactinella, Aphrocallistes, Eurete, and Farrea.