Revision of Drepanothrix Sars, 1862 (Anomopoda: Macrothricidae), with the description of a new species from East Eurasia and discussion of the genus-specific phylogenetic position and macrothricid paraphyly based on a mitogenome study

Drepanothrix Sars, 1862 is a monotypic genus of uncertain position within the family Macrothricidae (Cladocera: Anomopoda). Gamogenetic stages of Drepanothrix are poorly described despite the importance of their characters for anomopod systematics. Drepanothrix dentata (Eurén, 1861) is widespread in the Holarctic, but the conspecificity of its populations from different regions has not yet been proved. This study revises the diversity and phylogenetic position of Drepanothrix using morphological criteria, a molecular study based on three genetic loci (COI, 16S rRNA, ITS1), and mitogenomics. Our results show that East Eurasian populations of Drepanothrix represent a particular species, D. asiatica sp. nov., which differs from D. dentata by an absent or reduced dorsal tooth and by the male postabdominal morphology. The study of three gene fragments confirms the differentiation of the two species and assigns Nearctic specimens to a separate clade. Even with new morphological data, the position of Drepanothrix within Macrothricidae remains unresolved. The simple structure of limb I inner endite anterior setae, six setae in filtering comb of limb II gnathobase, and limb II exopodite bearing three setae distinguish Drepanothrix from the subfamily Macrothricinae to which it was previously attributed. The separate position of Drepanothrix is also supported by mitochondrial genomic data, including its mitochondrial genome structure.