A reappraisal of the Scaridiidae (Rotifera, Monogononta)

The morphology, systematics and distribution of the rotifer genus Scaridium Ehrenberg, 1830 are revised. The genus is transferred from Notommatidae to Scaridiidae, which is reinstated. In all, five species are recognized, two of which, S. montanum sp. n. and S. grandis sp. n., are new to science. Descriptions, a brief biometrical analysis and a key to the species are provided. Scaridium longicaudum (O.F. Muller, 1786) is cosmopolitic, S. bostjani Daems & Dumont, 1974 is probably a cosmopolitic warm stenotherm, S. elegans Segers & De Meester, 1994 is pantropic, S. montanum sp. n. occurs in the Mediterranean region and S. grandis sp. n. is recorded from Cameroon, Nigeria and Thailand.