Two new species of Achaeta (Enchytraeidae, Oligochaeta) from afforested post-mining and post-fire sites in Poland

Abstract

Achaeta (Enchytraeidae, Oligochaeta, Clitellata) is a genus of small, soil-dwelling annelids, peculiar by the absence of chaetae in all species. Here two new species of this genus are described from afforestation sites in southern Poland. Descriptions are based on the investigation of living and preserved material. The species are also characterized at the DNA level, using fragments of the COI and ITS genes, sequenced from the holotypes and paratypes. The worms are not longer than 4–6 mm, with about 30 to 35 segments, and with medium-large male and female reproductive organs. Achaeta florens sp. nov., discovered at a post-mining site, has four segmental pyriform glands, an oesophageal appendage restricted to segment V, a clitellum with distinct transverse rows and dorsal and ventral interruption, and spermathecae with blossom-like fields of vesicular gland cell apices around the ventrally located ectal pores. The species is without peculiar characters but the combination of characters is diagnostic. Its morphological distinction from A. nurmineni, described from the Indian subcontinent, is difficult due to the poor description of that species; A. nurmineni is therefore considered a species inquirenda. Achaeta gemmata sp. nov., discovered in high abundance at a post-fire site, is without pyriform glands but with conspicuous, gem-like lateral papillae in all preclitellar segments. The papillae are modified and enlarged epidermal gland cells that protrude into the body cavity. The species is without oesophageal appendage and has a dorsally closed clitellum and lateral spermathecal pores. It is superficially similar to Achaeta camerani, found at the same site, but can be distinguished based on sexual and non-sexual characters. A comparison of COI sequences showed 100% identity with a specimen from Sweden, erroneously identified as A. cf. brevivasa. Genetic distance between the two new species based on COI differences is 20%, distances to other species of Achaeta with publicly available COI sequences range from 16% to 26%.