Trapped on the Roof of the World: taxonomic diversity and evolutionary patterns of Tibetan Plateau endemic freshwater snails (Gastropoda: Lymnaeidae: Tibetoradix).

The high-elevation Tibetan Plateau (western China) is inhabited by a unique, though not particularly species-rich, community of organisms. We explored the species content and evolutionary history of the Tibetan Plateau endemic freshwater snail genus Tibetoradix. Phylogenetic relationships within the genus were reconstructed based on available sequence data. We used a single-rate Poisson Tree Processes approach for species delimitation and compared putative species-level clades with already described taxa. We found that the genus consists of at least 6 species, of which we described 4 as new to science. Shell and soft body morphology was examined and the radula in Tibetoradix was described for the first time. Based on our findings, the diversification of the genus did not result in a prominent morphological differentiation and a number of species can be regarded as morphologically cryptic. Single species found in different drainage areas indicate relatively good passive dispersal abilities of the snails. The allopatric distribution of the species could result from competitive exclusion between them. The absence of Tibetoradix spp. outside the Tibetan Plateau could be explained by a scenario of an "evolutionary trap", where adaptations to high elevation conditions prevented the taxa from a successful colonization of lower elevations.

Redescription of Leptogyra bujnitzkii (Gorbunov, 1946) comb. nov., the first representative of the gastropod subclass Neomphaliones from the high Arctic.

Ganesa bujnitzkii Gorbunov, 1946 was described from the bathyal of the Arctic Ocean north to the Laptev Sea based on only two specimens, which were the only representatives of this species mentioned by Gorbunov (1946b). Galkin (1955) noted that the shell sculpture of Ganesa bujnitzkii is similar to that of Cyclostrema valvatiodes (Jeffreys, 1883), and that the radula of the G. bujnitzkii differs from other species of the genus Ganesa Jeffreys, 1883 and members of the family Trochidae. Later, based on the original description, Warén (1993) proposed that the species may belong to the genus Skenea; however, he did not examine the type specimen. This opinion was reiterated by Kantor Sysoev (2006).

Redescription of Admete sadko Gorbunov, 1946 (Gastropoda: Cancellariidae).

Five species of the family Cancellariidae are currently known from Arctic seas: Admete contabulata Friele, 1879, A. clivicola Høisæter, 2011, A. solida (Aurivillius, 1885), A. viridula (Fabricius, 1780) and Iphinopsis inflata (Friele, 1879) (Golikov et al. 2001; Kantor Sysoev 2006; Høisæter 2011). Admete contabulata, A. clivicola and Iphinopsis inflata are only known from the Atlantic part of the Arctic, i.e. Norwegian and southwestern Barents seas (Høisæter 2011; Nekhaev 2014). Admete solida has been rarely reported since its first description from the Bering Strait (Sysoev Kantor 2002), however Nekhaev Krol (2017) recently reported a specimen from the eastern region of the Barents Sea that is similar in morphology to the holotype of this species. Admete viridula is the only representative of Admete reported from Siberian seas (Golikov et al. 2001; Lyubin 2003; Kantor Sysoev, 2006).

A new species of Menestho Møller, 1842 from the Arctic with remarks on Menestho albula (Fabricius, 1780)(Gastropoda: Heterobranchia: Pyramidellidae).

North Atlantic and Arctic representatives of the family Pyramidellidae had been intensively studied during the last decades. A valuable contribution was made by Warén (1989; 1991; 1993), who partially revised several genera from the Scandinavian waters. Norwegian representatives of the family were reviewed by Høisæter (2014). Distribution and diagnostic of many species had been specified by Schander (1995) and Nekhaev (2011; 2014; 2017). However, in the Eurasian Arctic Seas (except for the SW Barents Sea) only five species of Pyramidellidae had been recorded (Golikov et al. 2001; Kantor & Sysoev 2006; Nekhaev 2017): Liostomia eburnea (Stimpson, 1851), Chrysallida sublustris (Friele, 1886), Amaura candida (Møller, 1842), Amaura arctica (Dall et Bartsch, 1909) and Menestho truncatula Odhner, 1915.

Endemics or strangers? The integrative re-appraisal of taxonomy and phylogeny of the Greenland Lymnaeidae (Mollusca: Gastropoda).

The Lymnaeidae constitute a significant part of the freshwater molluscan diversity of Greenland. Since 1842, not less than 10 nominal taxa of the species and variety rank were described to organize the diversity of the Greenland lymnaeid snails. All previous attempts to revise these taxa were systematically based on morphological evidence only. Here, we provide a molecular analysis of the phylogenetic affinity and systematic status of three alleged species of the Greenland Lymnaeidae: Lymnaea vahlii (Møller, 1842), L. holboellii (Møller, 1842), and L. pingelii (Møller, 1842). We examined the newly collected material and inspected the type series of the three species. Our results show a very tight relationship between the Greenland snails and the Nearctic species Ladislavella catascopium (Say, 1817) s. lato. From the genetic point of view, the Greenland populations should be classified within L. catascopium, albeit probably with the merit of a subspecies status. The three nominal species of lymnaeids described by Møller (1842) are apparently synonyms of each other. Our findings assume a rather recent colonization of Greenland by snails arriving from the North American mainland, which is compatible with the so-called "tabula rasa" hypothesis, proposed to explain the currently observed taxonomic diversity of continental animals and plants of the North Atlantic islands. No lymnaeid species endemic to Greenland is thus revealed.

Morphology and systematic position of Cingula tumidula G.O. Sars, 1878 Gastropoda: Rissoidae).

Rissoidae is a family of small to minute marine gastropods distributed worldwide. The generic composition of the family was revised by Ponder (1984) based on characters of external morphology and internal anatomy. However, species level taxonomy within the family is still based mainly on conchological characters, which are less informative and usually not sufficient for resolving the systematic relationships of species. Northern Atlantic representatives of the family were revised by Warén (1974; 1996) and Bouchet & Warén (1993) based on shape and sculpture of both proto- and teleoconch, and were suggested to be members of several genera, widely distributed in boreal or even tropical Atlantic environments. These include Alvania Risso, 1826; Onoba H. & A. Adams, 1852; Obtusella Cossmann, 1921 and a few more. However, it was recently demonstrated that some these genera are not monophyletic (Criscione et al. 2016).