Redescriptions of three Milnesium Doyere, 1840 taxa (Tardigrada: Eutardigrada: Milnesiidae), including the nominal species for the genus

摘要

In this paper we redescribe two species (Milnesium eurystomum Maucci, 1991 and Milnesium tardigradum Doyere, 1840) and one subspecies (Milnesium tardigradum granulatum Ramazzotti, 1962), which we elevate to the species level. We establish a new type series for M. tardigradum sensu stricto along with the sequences of the cytochrome c oxidase subunit I (COI) and the internal transcribed spacer 2 region (ITS2). Moreover, we define two species groups within the genus based on the appearance of the dorso-lateral cuticle (the tardigradum and the granulatum group, with smooth and reticulated cuticle, respectively) and propose a system for denotation of the number of points on secondary branches of claws in the genus. We also provide a diagnostic key to alldescribed Milnesium species and discuss the world distribution of the genus.