Integrative taxonomy elucidates phylogenetic position of a clawless African eutardigrade (Tardigrada) supporting the erection of a new genus

Abstract

Abstract In the presented study, we re-investigated the soil-dwelling clawless tardigrade species Apodibius nuntius (Binda, 1984) using an integrative taxonomic approach. Our analysis is based on detailed morphological comparisons between three populations from three different countries: Mozambique (type population), Australia and Uganda. The first two populations comprise historical specimens deposited in museum collections, whereas the third one is newly found and reported for the first time in this study. In addition to morphological analysis, we constructed a phylogenetic tree of Isohypsibioidea using two ribosomal gene fragments (18S rRNA and 28S rRNA). The obtained results enabled us to establish a new genus, Sinunguibius gen. nov., which is assigned to the family Hexapodibiidae. The new genus constitutes the second known genus within Eutardigrada characterized by a complete absence of claws. The main morphological chacter that differentiates the new genus from the also clawless genus Apodibius is the number of placoids in the pharynx. Our results suggest that the complete loss of claws is a convergent trait that occurs in at least two families: Doryphoribiidae and Hexapodibiidae. The inclusion of the new genus within the family Hexapodibiidae required a corresponding amendment to its family diagnosis.