Synopsis of gastropod-associated nematodes of Ciscaucasia (Russian Federation) with the description of a new species of Pellioditis Dougherty, 1953 (syn. Phasmarhabditis Andrássy, 1976)

Caucasus is known as one of the few biodiversity hotspots in Europe and is characterised by rich gastropod fauna while the nematode fauna in association with gastropods has remained largely understudied. Surveys conducted in 2019 and 2021 in the North Caucasus of the Russian Federation (Stavropol Upland and western and central parts of Krasnodar Krai) has revealed the presence of three new species of Pellioditis, a facultative parasite of land gastropods, and two species of obligate parasites, the intestinal parasite Angiostoma kimmeriense and a new, still undescribed species of a larval ectoparasite Alloionema sp. The new associations of Cruznema sp. and Rhabditophanes sp. with land gastropods were recorded for the first time in the Russian Federation. The new species of Pellioditis Dougherty, 1953 described here is based on the analysis of morphology and molecular studies of two distant and morphologically distinct strains, thermalis and sindicae. Pellioditis thermalis n. sp. was characterised by females possessing a tail of about 95-100 mu m long, broadly conical in shape in the thermalis and sindicae strains, with a rounded anterior part and a subulate terminal part as long as the former; prominent phasmids located at the mid-tail, equatorial vulva position, a lateral field of three ridges (four incisions), males with spicules featuring a hole at the distal tip, ensheathed infective juveniles with average length 717 mu m in the thermals strain and 771 mu m in the sindicae strain, and exsheathed ones 644 mu m and 682 mu m, respectively. ITS-based phylogenetic analyses revealed that all Pellioditis species found in Ciscaucasia and Transcaucasia probably belong to two separate clades, with independent evolutionary histories of colonisation of this area. The entire Caucasus range area appears to serve as a biodiversity hotspot for the genus Pellioditis, presumably due to its complicated geological history and repeated isolation events for its terrestrial mollusc hosts.

Automated summary

Caucasus is a biodiversity hotspot in Europe known for its rich gastropod fauna. The nematode fauna associated with gastropods in this region has been understudied. Recent surveys conducted in the North Caucasus of Russia discovered three new species of Pellioditis, a parasite of land gastropods, as well as other previously unrecorded species. Molecular studies indicate that the identified Pellioditis species likely belong to two separate clades with independent evolutionary histories.