Tachira Chertoprud, Palatov & Vinarski, 2021

Chertoprud, Elizaveta M., Palatov, Dmitri M. & Vinarski, Maxim V., 2021, Revealing the stygobiont and crenobiont Mollusca biodiversity hotspot in the Caucasus: Part III. Revision of stygobiont microsnails (Mollusca: Gastropoda: Hydrobiidae) from the Russian part of Western Transcaucasia, with the description of new taxa, Zootaxa 5005 (3), pp. 257-275 : 272

Genus Tachira Chertoprud, Palatov & Vinarski , gen. nov.

Type species. Geyeria valvataeformis Starobogatov, 1962

Gender. Feminine.

Diagnosis. Shell small, low-conical, with convex whorls separated by oblique suture. Aperture ovoid. Umbilicus wide. Protoconch low domed-shaped, with pitted sculpture. Irregular pits turn into short wrinkles towards the end of the first whorl. Surface of teleoconch covered by rather rough growth lines. Operculum thin, paucispiral with submarginal nucleus, repeats shape of the peristome, edge corresponding to inner peristome lip rather straight, outer one—more convex. Radula : taenioglossate. Rachis with 4–5 cusps on each side of the median cusp and one pair of basal cusps, basal tongue narrow, V-shaped; lateral tooth with nine or eleven cusps (4 or 5 at the inner side, one largest, 4 or 5 at the outer side); inner marginal tooth with 18–20 cusps, outer marginal tooth with 14 cusps ( Fig. 6O ). Penis narrow, triangular in shape, and simple, without outgrowth. Animal blind, with depigmented body ( Fig. 6P ).

From all genera of the Caucasian hydrobiid snails, established to date, Tachira gen. nov. differs by a unique combination of general shell shape and the penis structure. The structure of the male reproductive system differs in shape from the conchologically similar genera Plagigeyeria Tomlin, 1930 and Caucasogeyeria Grego & Mumladze, 2020 .

Etymology. Named after the type locality of the type species—Takhira (or Krasnoaleksandrovskaya) Cave.

Species composition. A monotypic genus.

Takhira valvataeformis ( Starobogatov, 1962) , stat. nov.

( Fig. 6K–R ; Tables 2, 4)

Geyeria valvataeformis Starobogatov, 1962: 48-49 , fig. 1 (Ж); Vinarski & Kantor, 2016: 216; Grego et al., 2020: 41. Plagigeyeria valvataeformis Sitnikova et al., 2017: 278 , fig. 9, L.

Description. Shell relatively small (SH <1.65 mm), low-conical, thin. Body whorl height constitutes 0.68–0.80 SH, rather convex. Spire high, SH/SH ratio up to 0.67. Whorl number up to 4.25. Whorls rounded and visibly convex, separated by a deep oblique suture.Aperture rounded ovoid, completely separated from body whorl wall. Umbilicus wide. Protoconch broad (up to 381 μm in diameter), low dome-shaped, consisting of 1.4–1.5 whorls. WE 170–196 μm. Sculpture pitted with wrinkles. Protoconch separated from teleoconch by distinct growth stop line. Operculum thin, paucispiral with submarginal nucleus, with low rough thickening of nucleus area on the inner side. Edge corresponding to inner peristome lip rather straight, outer one—more convex. Penis bent, triangular in shape, without outgrowth, tapering in its distal part (see Fig. 6P ).

Type locality. Russia, Krasnodar Krai, Lazarevsky District, Krasnoaleksandrovskaya (= Takhira) cave. 44°00′56.67″N 39°21′48.6″E 173 m a.s.l.

Holotype. Lost ( Sitnikova et al., 2017). Shell dimensions of the holotype, mm (after Starobogatov, 1962): SH 1.40; SW 0.85; AH 0.55; AW 0.42.

Topotypes. Collected by D. Palatov, 5 th July 2020; wet material (1 under No. 1/ 503-2021 in ZIN) and empty shells (2 under No. 2/ 503-2021 in ZIN) .

Habitat and distribution. Endemic of Krasnodar Krai. Known only from the type locality. Inhabits a subterranean brook in Krasnoalersandrovskaya Cave together with Schapsugia pulcherrima comb. n. ( Fig. 1C ). Mollusks were collected from solid substrates especially from submerged stones. Population density is low, living snails are rare and can be collected only in the depths of the cave. In the cave brook sediments, there are found small quantities of empty shells of this species .

Figures

FIGURE 1. Geographic position of the type localities of Schapsugia kudepsta sp. nov. (1), Sch. pulcherrima and Tachira valvataeformis (2), and Sch. occultata sp. nov. (3). A—map of the north-western Greater Caucasus showing the type localities of spe- cies discussed in this paper; B—a small spring in the floodplain of the Kudepsta River; C—Krasnoaleksandrovskaya (Takhira) Cave; D—Tigrovaya Cave; E—the source of the Natashinsky Spring.

FIGURE 6. Schapsugia pulcherrima (A–J) and Tachira valvataeformis (K–R). A, B, K, L—shell; C, M—operculum: inner and outer sides; E, O—radulae; F–H, P—penis structure; D, N—protoconch, lateral view; J, Q—protoconch surface sculpture; I, R—protoconch, apical view. F, G correspond to individuals identified as ‘Paladilhiopsis orientalis’, H—‘P. pulcherrima’. White arrow points to the fin-like edging of the penis. Scale bars: A, B, J, K—500 μm; R—200 μm; F, G, H, K, L—250 μm; C, D, I, M, N—100 μm; E, J, Q—20 μm; O—10 μm.