Hiding in the Arctic and in mountains: a (dis)entangled classification of Claxtonia (Heterotardigrada: Echiniscidae)

Abstract

Abstract Numerous evolutionary lineages representing an armoured, limno-terrestrial family Echiniscidae are restricted to high mountainous or polar localities, exhibiting clear cold stenothermic preferences. One such group is the genus Claxtonia, with its type species Claxtonia wendti, originally described from Svalbard and later on reported globally. In this paper, we re-describe this taxon by establishing the neotype from Spitsbergen. We sequenced five genetic markers (18S rRNA, 28S rRNA, ITS-1, ITS-2, and COI) for multiple populations of Claxtonia, including C. mauccii, C. molluscorum, C. wendti, and several potentially new species, collected in the Alps, Andes, Carpathians, Scotland, Iceland, Southern Appalachians, Spitsbergen, Scandinavian Peninsula, Borneo, and the West Indies. The relationships between these species are elucidated thanks to the phylogenetic reconstructions based on nuclear loci. Various Claxtonia species frequently co-occur in mosses and lichens, which hampers delineating their probable geographic ranges. All historical records of C. wendti are questioned in the light of our revision. Delineation of new species within the genus is nipped in the bud due to numerous problems with original species descriptions, unknown intraspecific (including ontogenetic) variability, and the lack of DNA barcodes. Finally, it is hypothesized that Claxtonia potentially comprises two lineages: a cold-stenothermic one and a thermophilic subtropical–tropical one.