A comprehensive and integrative re-description of Synchaeta oblonga and its relationship to Synchaeta tremula , Synchaeta rufina and Synchaeta littoralis (Rotifera: Monogononta)

A comprehensive re-description of the monogonont rotifer Synchaeta oblonga Ehrenberg, 1832 is presented with the aim of creating a specific and robust suite of characters to identify this species that takes account of its morphological intraspecific variability. To accomplish this, we used an integrative approach that combined morphological data of the habitus and trophi (light and scanning electron microscopy) together with ecological and molecular data to generate a data set that clearly delineates S. oblonga from the morphologically similar Synchaeta tremula (Muller, 1786) with which it is often confused. In addition, by comparing S. oblonga to all remaining members of the genus Synchaeta, we found that the literature descriptions of Synchaeta rufina Kutikova and Vasiljeva, 1982, a Lake Baikal endemic species, and Synchaeta littoralis Rousselet, 1902, a species whose taxonomic status with respect to S. oblonga had already been called into question, to both lie entirely within the range of intraspecific morphological variability present in S. oblonga. Thus, we conclude that S. oblonga can be clearly demarcated from S. tremula, but that no unambiguous morphological differences exist to delineate it from either S. rufina or S. littoralis. Because our molecular data indicate S. oblonga to be a single species despite the morphological intraspecific variability that is present, we recommend that thorough re-examinations of the taxonomic statuses of both S. rufina and S. littoralis should be performed on topotypes sampled from their type localities (Lake Baikal, Russia and Dundee, Scotland, respectively).