A deceitful claw: Erection of Synonyx gen. nov. and Synonyxidae fam. nov. in Hypsibioidea (Eutardigrada: Parachela)

Claws are strongly sclerotised elements of tardigrade exoskeleton of a great phylogenetic and taxonomic importance. Although several general claw curvatures and anatomies can be distinguished within Eutardigrada, some more subtle differences in claw architecture have evaded the attention of taxonomists and have caused profound errors in species classification. Our study exposes a particularly deceitful morphotype and its results have widespread consequences for parachelan systematics, affecting two of the three major superfamilies in the order. Specifically, we analysed integratively 26 populations representing the Ursulinius cameruni complex from India and multiple locations in Australasia. Our genetic and morphological analyses demonstrate that this evolutionary lineage does not belong in Isohypsibioidea, but in Hypsibioidea. Moreover, some other taxa previously classified in different hypsibioid families are transferred to the new lineage. Specifically, Synonyxidae fam. nov. and Synonyxgen. nov. are established to accommodate the unique claw and cuticular morphotype of the Ursulinius cameruni complex. Also, Synonyx panjurliisp. nov., the type species for the new genus, is described from India, and two further hypsibioidean species are transferred from other genera to Synonyxgen. nov.: S. antonovaecomb. nov. (formerly Hypsibiidae: Hypsibius) and S. gibbosuscomb. nov. (formerly Acutuncidae: Mixibius). All these systematic changes clearly reflect the difficulties associated with a proper interpretation of claw structure in this peculiar phylogenetic linage. The evolution of Synonyxidae fam. nov. in Hypsibioidea is discussed in detail. Additionally, we elaborate on the taxonomic status and composition of Mixibius.