Haplosclerina Topsent (Porifera, Demospongiae) are here newly defined in a new content, although this follows earlier proposals for a subdivision of Haplosclerida at the ordinal level made by Bergquist (1980a). In the present concept, Haplosclerina Topsent, 1928c are marine Haplosclerida characterized by the possession of a regular anisotropic skeleton, in which primary ascending spicule tracts or fibres are invariably recognizable, even in unispicular skeletons. In this respect they differ from the suborder Petrosina, which has the skeleton isotropically organized. Spicules are smooth oxeas or strongyles in a single size category (Petrosina frequently have differentiated size categories). A further difference, which appears to be valid after exhaustive testing, is the viviparous reproduction (Petrosina are probably all oviparous). Haplosclerina differ from freshwater sponges that show some similarities, here united in the suborder Spongillina Manconi & Pronzato, in having a tangential ectosomal skeleton (with few exceptions), and by the lack of special microscleres protecting the gemmules. Also, spicules in Spongillina are frequently spined. Three families, Chalinidae, Callyspongiidae and Niphatidae, are recognized, differing in the organization of the skeleton. Chalinidae have a unispicular ectosomal skeleton and a lightly built paucispicular choanosomal skeleton; Callyspongiidae have a two-dimensional, often double- or triple-meshed ectosomal skeleton and usually a rectangular-meshed spongin-rich choanosomal skeleton; Niphatidae have a three-dimensional, often irregular ectosomal skeleton, and a pauci- or more often multispicular choanosomal skeleton, with strong primary fibres or tracts.