Order Heteractinida Hinde, 1887

Abstract

Heteractinida (Calcarea) are characterised by a calcareous spicule type known as the octactine, with six rays in one plane and two others at right angles to this plane. All genera of heteractinids are reviewed and illustrated, and keys provided for their identification. The group is known from the Early Cambrian to the end-Palaeozoic extinction, and includes 20 valid genera in four families. The new family Nuchidae is established. Geographical and stratigraphic distribution is summarised. A brief history of research on the group is offered.