Description of Bryceella perpusilla n. sp. (Monogononta: Proalidae), a New Rotifer Species from Terrestrial Mosses, with Notes on the Ground Plan of Bryceella Remane, 1929

Abstract

We here describe the new proalid rotifer species Bryceella perpusilla n. sp. on the basis of light and electron microscopy. The species, certainly representing one of the smallest rotifer and even metazoan species at all, was obtained in January 2008 from terrestrial mosses of North-west Germany. Bryceella perpusilla n. sp. is distinguished from other species of the genus by the very small size, the slender body outline, the short apical styli, the triangular rostrum, the outward curving, blunt and rod-shaped toes, the four-nucleated vitellogermarium, the slender manubria and the caudally directed alulae. With our observations, that can be used for future cladistic analyses of the Proalidae, we are able to define the generic diagnosis of Bryceella more precisely and to give an adapted species key. IntroductionThe phylum Rotifera is an astonishingly diverse group of aquatic microinvertebrates, rarely exceeding 0.5 mm, that contains more than 2,000 known species worldwide (WAL- LACE et al., 2006;SEGERS, 2007). The representatives inhabit all kinds of water environments. The monogonont taxon Proalidae is a polyphyletic group (see WILTS et al., 2009a; DE SMET, in press.) of about 50 species that occur free-living, parasitic or epizoic in freshwater, saline water or moist terrestrial habitats. Within Proalidae, one of the smallest genera is Bryceella REMANE, 1929 currently containing only two species following DE SMET (1996) and the most recent rotifer checklist published by SEGERS (2007): Bryceella stylata (MILNE, 1886) and Bryceella tenella (BRYCE, 1897). The species occur in different aquatic and semiaquatic habitats like moors, the psammon of acid waters, mosses and leaf litter. Although new data on the morphology of Bryceella stylata have been published recently (WILTS et al., 2009b, WILTS et al., 2010, our knowledge of B. tenella remains insufficient. This particularly also * Corresponding author 472 E. F. WILTS et al.