Novel integrative data for two Milnesium Doyère, 1840 (Tardigrada: Apochela) species from Central Asia

Abstract

Tardigrada are a phylum of microscopic animals inhabiting a variety of ecosystems, both aquatic and terrestrial, being recognised for their remarkable abilities to withstand tough environmental conditions. The order Apochela groups exclusively carnivorous species, with the vast majority representing the genus Milnesium Doyère, 1840. Representatives of this genus are characterised by simplified morphology, therefore possessing an extremely limited set of taxonomically meaningful morphological traits. Nevertheless, the taxonomy of Milnesium is mostly based on classical data: observations and measurements in light microscopy with the majority of descriptions lacking integrative data, most importantly DNA barcodes, but also scanning electron microscopy photographs and developmental variability analysis. Hence, re-descriptions that include novel integrative data are urgently needed. In this contribution, we provide new taxonomic data for two species described from Central Asia, Milnesium almatyense (a single population) and Milnesium reductum Tumanov, 2006 (five populations): morphometrics, DNA barcodes, SEM observations and description of developmental variability. As a result, we amend the description of both species and reveal phylogenetic relationships of those species and other sequenced congeners. The integrative data confirm the validity of the two species and include them in the growing set of Milnesium species associated with DNA sequences.