Integrative analysis of Minibiotus jonesorum Meyer et al., 2011 (Eutardigrada: Macrobiotidae) exposes intraspecific variability in microplacoid development

Abstract The taxonomy of tardigrades has undergone significant changes over the past two decades, primarily due to the introduction of molecular techniques. However, despite the dynamic development of this branch of zoology, the phylogenetic position of most species remains unknown, indicating the continued need for integrative descriptions and redescriptions. A notable example is the genus Minibiotus , of which morphologically diversity raises the possibility of its polyphyly. However, the extremely limited genetic data and frequent lack of detailed morphological information hinder the verification of relationships within this genus. In this study, we provide an integrative analysis of Minibiotus jonesorum based on a newly discovered population from Devil’s Lake State Park, Baraboo, Wisconsin, USA. Our approach combines traditional taxonomic methods, including morphological and morphometric analyses using light and scanning electron microscopy, alongside genetic data for four markers: three nuclear markers (18S rRNA, 28S rRNA, ITS-2) and one mitochondrial marker (COI). Thanks to the discovery of a new population and a re-examination of the type series, we reveal new traits and update the description and the differential diagnosis of M. jonesorum . Importantly, we show that the microplacoid, a taxonomical important trait in many eutardigrade lineages, can be absent or developed to different extents within a single species. Additionally, for the first time, we constructed a concatenated phylogenetic tree for all available sequences of the genus Minibiotus using Bayesian inference, which provides new insights into the enigmatic evolution of the genus.