Discordance of genetic diversification between deep- and shallow-water species of Kobeltocochlea Lindholm, 1909 (Caenogastropoda: Truncatelloidea: Benedictiidae) endemic to Lake Baikal with the description of a new species, review of the genus, and notes on its origin

We describe a new species, Kobeltocochlea tamarae Sitnikova, Teterina & Maximova sp. nov., from Lake Baikal discovered in the Saint Petersburg methane seep at a depth of approximately 1400 m. The uncorrected genetic distance was 4.26% of the COI gene between this new species and K. falsipumyla collected from the Academic Ridge at depths between 157 and 163 m. The two shallow-water species, K. martensiana and K. olchonensis, differed in substrate preference and geographic habitats, with a genetic distance of 0.97% for COI. Phylogenetic analysis of mitochondrial (COI, 16S) and nuclear (ITSI, 28S) sequences indicated that Kobeltocochlea was paraphyletic with respect to other benedictiid genera Benedictia and Yaroslawiella, formed well-supported monophyletic groups. We revealed the discordance of morphological and genetic data within Kobeltocochlea and other benedictiids, which reflected their complicated history. The current knowledge of benedictiids does not allow for significant changes in the taxonomy of the Benedictiidae, except for synonymizing K. lindholmiana with K. olchonensis and Pseudobenedictia with Benedictia that were also investigated. We speculate that three main lineages of benedictiids originated from three populations of a single ancient species approximately 3.2 Ma. The speciation of deep-water species was probably driven independently by bathymetric isolation in the cold methane seeps of different geomorphological structures. The diversification of the third lineage consisting of littoral (including K. martensiana/K. olchonensis), deep-water, and eurybathic benedictiids may be explained by rapid adaptive radiation to intralacustrine environments.