The diversity and distribution of freshwater molluscs is poorly studied in the Republic of Georgia, due to the scarcity of field studies during the last 50 years. Here, we present the results of the first concerted investigation of freshwater mollusc biodiversity in the Javakheti Highlands, in the southern, mountainous region of Georgia. In total, we were able to collect 22 species from 42 sampling localities, including different kinds of freshwater habitats. Amongst the 22 collected species, 12 were recorded for the first time from Javakheti. From the newly-recorded species, Bathyomphalus contortus is a new country record, whose identity is supported by 16S rRNA sequence data.

The first comprehensive checklist of mayflies (Ephemeroptera) of Georgia is provided based on literature data supplemented by our unpublished data, including extensive samples in 2013-2017, works with the collections and types, faunistic observations, and taxonomical contributions. Records of 75 species are provided, with one species reported as a new finding for the country. Notes about the taxonomic status of several species are given. The present contribution represents the first publication of this kind for mayflies within the whole Caucasus area.

First records of invasive bivalve freshwater mollusc species Mytilopsis leucophaeata (Conrad, 1831) and Corbicula fluminalis (O. F. Müller, 1774) in Georgia are reported. No native or alien extant dreissenid species have ever been recorded form this region so far. A finding of C. fluminalis in Georgia is also a new record for the country though this species inhabits the rivers of adjacent Azerbaijan. Apart from two mentioned bivalve molluscs three non-indigenous gastropod species are registered from Georgia: freshwater Ferrisia californica (Rowell, 1863) and Physella acuta (Draparnaud, 1805) and land snail Eobania vermiculata (O. F. Müller, 1774).

The representatives of the genus Ametropus (Insecta, Ephemeroptera) were recorded 80 years ago in Georgia. Due to the taxonomic uncertainty, the recorded specimens were considered potentially new taxa. Since then, no other record of Ametropus has been documented from the whole South Caucasus and its nearby regions further south. In the present contribution, we provide a new record of Ametropus from the Alazani River (Kura River Basin, Georgia). Morphological and DNA barcoding of the COI gene fragment showed that the species belongs to the widespread Holarctic species A. fragilis. Morpho-anatomical characteristics also confirmed the high degree of similarity between the newly recorded specimens and those once recorded 80 years ago. In addition, the COI barcode showed a strikingly closer relationship between Caucasian A. fragilis and North American A. neavei (3.54% divergence) compared to Caucasian and European A. fragilis populations (4.3% divergence). The observed pattern clearly indicates the need for further and more thorough revision of the Ametropus species complex in the Holarctic region.

This study provides the first attempt to investigate the molecular diversity of South Caucasian freshwater molluscs (Mollusca, Gastropoda) and lay down the first bricks to build up a DNA-barcode library. In total, 289 COI barcode sequences were obtained from 33 morpho-species belonging to 24 molluscan genera and 10 families that represent nearly 30% of known freshwater molluscan diversity of the South Caucasus region. DNA barcodes were analysed by means of the Barcode Index Number (BIN) and the other tools available in BOLD Systems. Results showed that the knowledge of freshwater molluscs diversity in the South Caucasus is far from comprehensive. For the studied 33 morpho-species, 289 barcodes were clustered into 40 BINs, from which unique BINs were defined for 12 species and five species were characterised with more than a single BIN. From the studied taxa, 60% were characterised larger than 2.2% sequence divergence indicating high genetic variation or cryptic diversity. Within our limited taxonomic coverage, we found one new species for the Republic of Georgia (Galba schirazensis) and at least three undescribed species belonging to the genera Stagnicola, Segmentina and Anisus. Uniqueness and high molecular diversity of the studied species emphasise the need for further intensive morphological and molecular investigations of the South Caucasian freshwater molluscan fauna.