Family Tretodictyidae Schulze, 1886

Abstract

Tretodictyidae Schulze (Hexactinellida, Hexactinosida) is defined in accordance with Ijima’s 1927 formulation – basiphytous hexactinosans with a distinctive channelization pattern, schizorhyses, in a euretoid dictyonal framework. The family is revised to contain eight genera and 22 species, and many lectotype designations are made. With exception of removal of Auloplax to the Dactylocalycidae, this is essen- tially the same constituency adopted by Ijima. Genera are differentiated by a combination of body form and spiculation. Body form varies from the traditional funnel form of Hexactinella to cups, branching tubes, branching solid cylinders and globular forms without sym- metry. The family is world wide in distribution, with a restricted depth range of (11?)–90–1917m. The family is absent from very deep water communities, probably due to its requirement for hard bottom substrate.