Description of Lepidochaetus tirjakovae sp. nov. (Gastrotricha: Paucitubulatina: Chaetonotidae), using morphology and DNA barcoding.

Lepidochaetus is a phylogenetically interesting genus, as it represents one of the deepest branching lineages within the highly diverse family Chaetonotidae. Its taxonomy is, however, very complex due to multiple insufficient morphological descriptions, proposed synonymizations, and availability of molecular data for only two species. In the present study, we evaluated the morphological diversity of Lepidochaetus , and used DNA barcoding and Bayesian coalescent technique to delimit two closely related species, Lepidochaetus zelinkai and Lepidochaetus tirjakovae sp. nov. The new species was studied with differential interference contrast microscopy and morphometry. It differs from L. zelinkai especially by the number of scale types, the morphology of the dorsal subterminal median scale, and by the morphology of ventral scales. The genetic divergence between L. tirjakovae sp. nov. and L. zelinkai is 0.18% in 18S rDNA, 0.83% in 28S rDNA, and 3.05–4.48% in cytochrome c oxidase subunit I (COI). According to the present distance analyses, interspecies divergences within Chaetonotidae are 0.00–2.75% in 18S rDNA, 0.00–11.93% in 28S rDNA, and 3.05–21.86% in COI. As interspecies divergence thresholds are arbitrary, the utilization of Bayesian species delimitation along with detailed morphological investigations is recommended in the chaetonotid taxonomy. [ABSTRACT FROM AUTHOR]