Order Haplosclerida Topsent, 1928

Abstract

Haplosclerida Topsent (Demospongiae) is characterized by possession of an isodictyal skeleton of diactinal megascleres. The megascleres are relatively short fusiform oxeas, or short compact strongyles. Microscleres are restricted to microxeas/strongyles, sigmas, toxas, raphides and amphidiscs. The sigmas and toxas may be interpreted as a trait shared with the order Poecilosclerida. A large number of common shal- low-water marine sponges and all sponges occurring in freshwater are considered members of this order. To accommodate the high diver- sity of groups and habitats, and in acknowledgement of the continuing debate about monophyly of the order, three suborders are now recognized: Haplosclerina with families: Callyspongiidae, Chalinidae and Niphatidae; Petrosina with families Calcifibrospongiidae Petrosiidae and Phloeodictyidae; and Spongillina with families Spongillidae, Malawispongiidae, Metaniidae, Metschnikowiidae, Palaeospongillidae, Potamolepiidae and Lubomirskiidae. Haplosclerina and Petrosina appear closely related morphologically and are con- troversial higher taxa. They may be conveniently separated by the absence of a clear anisotropic skeletal structure and the apparent oviparous reproduction in Petrosina. Spongillina appear more distantly related and are characterized by absence of a tangential ectosomal skeleton, possession of spined megascleres and unique amphidisc microscleres, and gemmules with an elaborate anatomy and physiology.