The tardigrade Mesobiotus aradasi (Binda, Pilato & Lisi, 2005) is widely distributed along the Antarctic Peninsula

Antarctica is considered one of the most inhospitable places to life due to its low temperatures and lack of liquid water. However, meiofauna taxa such as tardigrades not only thrive, but also show remarkable biodiversity in this habitat. Tardigrades are a phylum of small animals (less than 1 mm in length) mainly known for their ability to withstand freezing and desiccation, which are common stressors in Antarctica. The tardigrade genus Mesobiotus is widely distributed and abundant in Antarctica, particularly in the Antarctic Peninsula, where it is been hypothesized it was present even before the continent froze. Different Mesobiotus species have been recorded from the Antarctic Peninsula, but most are based on DNA data and lack assignment to described species. We used integrative taxonomy methods (DNA and morphology combined) on a novel population of Mesobiotus aradasi from Antarctic Peninsula. The latter allowed us to link previous molecular and morphological records of this species and to build a comprehensive map of its distribution. We show that this species is present across almost all the Antarctic Peninsula, whereas there are no records of it for any other Antarctica region. This study highlights the importance of integrating molecular and morphological methodologies and their complementarity when working with biodiversity and distribution data. The M. aradasi distribution highlights its endemicity in the Antarctic Peninsula and calls for attention to possible future threats to this species.