Two new species of the Drawida japonica species complex (Oligochaeta, Moniligastridae) from East Asia delimited by integrative taxonomic methods

The <i>Drawida japonica</i> (Michaelsen, 1892) species complex is a cosmopolitan earthworm group that is widely distributed throughout Asia, and has a high degree of diversity. Nonetheless, the species composition of this species complex remains ambiguous due to limited taxonomic investigation. An integrative taxonomic approach, incorporating both morphological and molecular datasets, is herein applied to elucidate the <i>D. japonica</i> species complex across East Asia, with the objective of delimiting putative new species. External and internal morphological characters were examined for taxonomic identification. For molecular phylogenetic analysis, one mitochondrial marker, the cytochrome c oxidase subunit I (COI), and three nuclear loci, namely 28S rRNA (28S), A-kinase anchor protein 17A (AKAP17), and flavin adenine dinucleotide synthetase 1 (FLAD1) were used. Species delimitation was performed using three complementary methodological frameworks: Assemble Species by Automatic Partitioning (ASAP), the Generalized Mixed Yule Coalescent (GMYC) phylogenetic approach, and Bayesian Phylogenetics and Phylogeography (BPP). Congruent species boundaries were recovered across all analyses, with the single exception of the GMYC model applied to the mitochondrial COI data set. Furthermore, the interspecific K2P genetic distance exceeded 15%. This study has delimited two new species, namely <i>D. henanensis</i> <b>sp. nov.</b> and <i>D. sinensis</i> <b>sp. nov.</b> The two new species represent the first additions to the species complex in the past decade, thereby significantly contributing to our understanding of <i>Drawida</i> earthworm diversity in Asia.