Order Amphidiscosida Schrammen, 1924

Abstract

Recent Amphidiscosida Schrammen (Hexactinellida: Amphidiscophora) consists of three families containing twelve genera, only one of which, Hyalonema, is divided into subgenera, presently numbering 12. The order is characterized by presence of amphidiscs and absence of hexasters as microscleres. All members are lophophytous, with body form varying from simple ovoid to cone, cup, cylinder, and bilat- erally symmetrical variants of these. Dermalia and atrialia are pinular pentactins and, rarely, hexactins; supporting hypodermalia and hypoatrialia are oxypentactins. Basal anchors, where known, are toothed monactins. Families are distinguished by form of main choanosomal megascleres: diactins in Hyalonematidae, pentactins in Pheronematidae, and tauactins in Monorhaphididae