Integrating DNA and morphological taxonomy to describe diversity in poorly studied microscopic animals: new species of the genus Abrochtha Bryce, 1910 (Rotifera: Bdelloidea: Philodinavidae)

Specimens of the bdelloid rotifer genus Abrochtha were collected from mountain and desert sites in the western USA. All were morphologically distinct from the two previously described species of this genus. Barcode sequences of the cytochrome c oxidase subunit I (COI) gene were obtained from 14 specimens. These were shown to be samples from four different independently evolving populations or metapopulations, i.e. evolutionary species. Two different species criteria rooted in population and evolutionary genetic theory, the 4¥ rule and the generalized mixed yule coalescent (GMYC) method, agreed in the delimitation of the four species. Three of these evolutionary species are formally described as new species; two are cryptic species, differentiable only by statistical analysis of morphometric data. This is the first time that these species criteria have been used in new species descriptions, and the first formal descriptions of cryptic bdelloid species delimited by molecular analyses.