A new species of the Amynthas corticis group with support from mitogenomic data and a new record of Metaphire agrestis (Goto & Hatai, 1899) (Oligochaeta, Megascolecidae) in northeastern China

As part of a series of investigations on earthworm diversity conducted in northeastern China in recent years, a new species, Amynthas dandongensis Han & Zhao, sp. nov., has been discovered. It belongs to the A. corticis species group characterized by having four pairs of spermathecal pores in segments 5 / 6 / 7 / 8 / 9. The new species mainly differs from the other members of the A. corticis species group by its relatively small body size and the absence of male pores and genital markings in both the spermathecal and male pore regions.

The interspecific pairwise COI genetic distances between A. dandongensis Han & Zhao, sp. nov. and the other closely related species ranged from 15 % to 22 %. Phylogenetic analyses using mitogenomic coding genes further explored the relationships within the A. corticis species group, clarifying the position of A. dandongensis Han & Zhao, sp. nov. in the group. Additionally, a new record of a cosmopolitan earthworm, Metaphire agrestis (= Amynthas agrestis) (Goto & Hatai, 1899) has been investigated in China.

New sequences from specimens collected in northeastern China were analyzed together with “ M. agrestis ” and “ A. agrestis ” sequences available from GenBank to further explore phylogeographic relationship. The dataset of all M. agrestis sequences showed intraspecific genetic distances of 0–1 %, consistent with the observed morphological similarities. Haplotype network analyses also revealed no genetic isolation among different populations of M. agrestis (= A. agrestis).

Moreover, re-examination of previous descriptions and illustrations of the male pores of agrestis indicates that this species should be assigned to the genus Metaphire Sims & Easton, 1872, rather than Amynthas Kinberg, 1867.