On the global distribution of microscopic animals: new worldwide data on bdelloid rotifers

The faunistic knowledge of the distribution of certain groups of microscopic animals is so small that it borders on total ignorance. The biogeographical patterns of protists and microscopic animals seem to differ from those of larger animals, with most species widely distributed. Nevertheless, few data are available for many groups of microscopic eukaryotes within otherwise well-studied areas such as Europe, let alone from remote areas. In this respect, bdelloid rotifers are one of the groups that is particularly understudied. This is mostly due to intrinsic taxonomic difficulties and ambiguities in the identification of these ancient asexual animals. Herein, we report 302 records of 61 species collected around the world, covering poorly known areas such as Mexico, Tanzania, and Australia, but also reporting new records for European countries. Some species have a cosmopolitan distribution, while others seem to be geographically limited to certain areas. We discuss the morphological, ecological, and biogeographical coherence of bdelloid species.