Northwestern China Amynthas study describes new species and subspecies

A taxonomic study of earthworms from northwestern China described Amynthas longnanensis as a new species and Amynthas pectiniferus guanzhongensis as a new subspecies. The study combined external and internal morphology, mitochondrial cytochrome c oxidase subunit I (COI) barcoding and complete mitochondrial genomes. Its mitochondrial phylogeny also indicated that the A. sieboldi species group, as currently defined, is not monophyletic.

The researchers collected specimens in July 2025 by digging and hand sorting in Gansu and Shaanxi provinces. They fixed the animals in 95% ethanol in the field and stored them at −20 °C for examination. The study analyzed seven clitellate specimens of A. longnanensis and one clitellate of A. pectiniferus guanzhongensis, with the type and other specimens deposited at Langfang Normal University in Hebei, China.

Both new taxa were assigned to the A. sieboldi group, whose members are characterized by three pairs of spermathecal pores in intersegments 6/7–8/9. A. longnanensis was represented by one holotype from Cheng County and six paratypes from Cheng and Hui counties in Longnan Prefecture, Gansu. The holotype of A. pectiniferus guanzhongensis came from Huazhou Park in Weinan Prefecture, Shaanxi, where it was collected from a lawn.

Amynthas longnanensis measured 112–169 millimetres long and 6–8 millimetres in diameter and had 67–107 segments. Diagnostic features included an epilobous prostomium, an annular clitellum on segments XIV–XVI, a first dorsal pore at 12/13, paired male pores in XVIII and paired intestinal caeca arising in XXVII and extending forward to XXIII. The caeca had five, rarely six, secondary branches, with the ventral branch longest. The authors distinguished the species from A. pectiniferus and other members of the group using differences in dorsal-pore position, papillae beside the male pores, intestinal-caeca structure and other anatomical characters.

The A. pectiniferus guanzhongensis holotype measured 107 millimetres long and 6 millimetres in diameter and had 107 segments. Its first dorsal pore was positioned at 13/14, whereas the nominate A. pectiniferus has its first dorsal pore at 12/13. The researchers also reported differences in the spermathecal ampulla duct, the form of the diverticulum stalk and intestinal-caeca structure. In the new subspecies, the stalk was medially folded and V-shaped, and the caeca were pinnate, with undulate margins on the first, third and fourth branches. In A. pectiniferus, the stalk was naturally curved without folding, while the caeca were digitate with smooth margins and even edges.

COI analysis found intraspecific distances of 0% to 2.1% within A. longnanensis. Distances between the new species and other sampled members of the A. sieboldi group ranged from 12.9% in comparison with A. pectiniferus to 20.7% in comparison with A. szechuanensis. The distance between A. pectiniferus guanzhongensis and nominate A. pectiniferus was 10.1%. Two complementary COI-based methods, the distance-based Assemble Species by Automatic Partitioning and the phylogenetic Generalized Mixed Yule Coalescent model, each divided the sequences into seven molecular operational taxonomic units consistent with the morphological classification and recognized A. longnanensis as a distinct unit.

The complete mitochondrial genome of A. longnanensis was 15,114 base pairs, while that of A. pectiniferus guanzhongensis was 14,571 base pairs. Each genome contained 37 genes: 13 protein-coding genes, two ribosomal RNA genes and 22 transfer RNA genes. Their gene arrangements matched those reported for other members of the A. sieboldi group and other megascolecids. Maximum-likelihood and Bayesian analyses used sequences from 13 mitochondrial protein-coding genes across 33 earthworm taxa, with Perionyx excavatus as the outgroup.

In both phylogenetic analyses, A. pectiniferus, A. moniliatus, A. longnanensis and A. pectiniferus guanzhongensis formed a strongly supported clade, with a maximum-likelihood bootstrap value of 92% and a Bayesian posterior probability of 100%. A. pectiniferus and A. pectiniferus guanzhongensis were resolved as sister lineages; A. longnanensis occupied the adjacent lineage, while A. moniliatus was basal to those three. Amynthas yunoshimensis and A. sieboldi clustered outside the four-taxon clade. The distinct placements of the new taxa were consistent with their morphological diagnoses and COI-based delimitation, while the broader tree indicated that the A. sieboldi group is not monophyletic.

The study provides the first formally recorded Amynthas species from Longnan and Gansu Province, addressing a geographic gap in a region whose megascolecid fauna remains poorly surveyed. However, the evidence is based on limited sampling, particularly the single specimen available for the new subspecies. The authors proposed that Pleistocene climatic oscillations may have contributed to isolation between A. pectiniferus in southeastern China and the new subspecies in the Weihe River Valley, but that explanation was not directly tested by the morphological or mitochondrial analyses. They conclude that broader surveys combining morphological and molecular data are needed to establish species composition, distribution boundaries and phylogenetic relationships in northwestern China.

Subject of Research: Taxonomic description and mitochondrial phylogeny of two new Amynthas earthworm taxa from northwestern China

Article Title: A new species and a new subspecies of Amynthas Kinberg, 1867 earthworms ( Oligochaeta , Megascolecidae ) from northwestern China with data from the mitochondrial genome

Article References: Liu, Q., Zhang, H., Li, C., Chen, Y., Zhang, Y., & Zhao, H. (2026). A new species and a new subspecies of Amynthas Kinberg, 1867 earthworms (Oligochaeta, Megascolecidae) from northwestern China with data from the mitochondrial genome. Subterranean Biology, 57, 139-159. https://doi.org/10.3897/subtbiol.57.198999

Image Credits: AI Generated

DOI: 10.3897/subtbiol.57.198999

Keywords: Amynthas, earthworms, new species, new subspecies, taxonomy, mitochondrial genomics, COI barcoding, species delimitation, phylogenetics, northwestern China, species, subspecies