Establishment of the Drawida gisti species complex and description of a new species from northeastern China (Oligochaeta, Moniligastridae).

Abstract

The family Moniligastridae Claus, 1880 remains taxonomically poorly resolved, and its actual species diversity is likely severely underestimated. Despite its ecological significance as an East Asian endemic species, Drawida gisti Michaelsen, 1931 has been studied almost exclusively from non-taxonomic perspectives. Consequently, its species boundaries remain poorly understood. Here, we formally establish the Drawida gisti species complex (DiSC), comprising eight morphologically and geographically related species. We employed an integrative taxonomic approach combining morphology and molecular data to examine specimens of DiSC from northeastern China, leading to the description of a new species, Drawida xuqini sp. nov. The new species is characterized by a colorless body in alcohol, 3-5 gizzards, M-shaped prostates, a very short and uncoiled vas deferens, and thick penes with a swollen base and blunt, rounded apex. Phylogenetic analyses based on 13 protein-coding genes of the mitochondrial genome of Drawida employing two molecular species delimitation methods-Assemble Species by Automatic Partitioning (ASAP), and Bayesian Phylogenetics and Phylogeography (BPP)-recovered D. xuqini sp. nov. as a monophyletic lineage, and COI genetic distances (19.4-22.0% between D. xuqini sp. nov. and D. gisti gisti) confirmed the species status of D. xuqini sp. nov. Additionally, we provide an updated redescription of D. gisti gisti based on newly examined specimens from multiple localities. Our findings highlight considerable external morphological plasticity in D. gisti gisti, which may likely be environmentally induced, and underscore the necessity of integrative approaches for accurate species delimitation in this group.