Schapsugia occultata 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 : 268

Schapsugia occultata Chertoprud, Palatov & Vinarski , sp. nov.

( Fig. 7J–R ; Tables 2, 4)

Description. Shell relatively small (SH <1.57 mm), thin-walled, conical-ovoid, relatively narrow (SW/SH ratio 0.47–0.53), whitish. Whorl number up to 4.60. Body whorl high (about 0.65 of SH), moderately inflated. Spire high, constitutes 0.62–0.70 SH. Aperture perfectly oval with evenly thickened inner lip which is not detached from body whorl wall. Umbilicus slit-like or even absent. Protoconch broad (up to 380 μm in diameter), low domed-shaped, on average consisting of 1.5 whorls. Initial part of the embryonic shell reaches 200 μm in diameter. Sculpture pitted with wrinkles. Embryonic shell separated from teleoconch by distinct line of growth stop. Surface of the teleoconch with rather frequent and prominent growth lines. Operculum ovoid, thin, whitish, and transparent, without thickening. Radula unknown. Penis with lateral lobe in medial part and bulged distal tip. Penial lobe blunt, triangular in shape, adheres to penis, and is directed towards its base. Distal-medial part of penis from lobe to tip has a harpoon-like shape with one blunt prong pointing backwards. Distal part bears fin-like edging consisting of thin and relatively fragile cells ( Fig. 7P ).

Holotype ( Fig. 7J , alcohol specimen): collected by E. Chertoprud, 23 th July 2020, No. 1/502–2021 ( ZIN). Shell dimensions of the holotype (mm): SH 1.4; SW 0.73; BWH 0.97; SpH 0.43; BWW 0.68; AH 0.5; AW 0.48.

Paratypes. 10 empty shells collected by D. Palatov, 23 th July 2020 (5 under No. 2/ 502–2021 in ZIN, 5 under No. Lc- 41084 in ZMMU) .

Type locality. Russia, Krasnodar Krai, Gelendzhiksky District, groundwaters in the source of Natashinsky spring. 44°31′26.68″N 38°17′40.82″E 167 m a.s.l.

Etymology. The name occultata (lat.) means “hidden” which characterizes the hard-to-reach habitat of this mollusc. We had to dig about a cubic meter of rocky ground in the spring source to find a couple of living specimens.

Habitat and distribution. Endemic to Krasnodar Krai. Known only from the type locality. Inhabits groundwaters in the source of Natashinsky Spring ( Fig. 1E ). We were able to find only a few living individuals on stones of the spring source. Most likely the population density is quite low, and most of the snails dwell deeper underground .

Differential diagnosis. Schapsugia occultata sp. nov. is the smallest representative of the genus. Shell is lower (SH up to 1.57 mm) and narrower (SW up to 0.78 mm) than in Sch. pulcherrima comb. nov. and Sch. kudepsta sp. nov. Aperture shape is perfectly oval like in Sch. kudepsta sp. nov. Sch. occultata sp. nov. and Sch. kudepsta sp. nov. share a similar harpoon-like structure of the penis with fin-like edging on the distal part. However, the penial tip of Sch. occultata sp. nov. is broader and bulgier. The medial lobe has the same location and direction in both species; however, in Sch. occultata sp. nov. it is broader in size and triangular in shape.

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 7. Schapsugia kudepsta sp. nov. (A–I) and Schapsugia occultata sp. nov. (J–R). A, J—shell, holotype; B, C, K, L—shell; D, M—protoconch, lateral view; E, N, O—protoconch surface sculpture; F—radula; G, P—penis structure; H, I, Q, R—protoconch, apical view. White arrow points to the fin-like edging of the penis. Scale bars: A–C, J–L—500 μm; G, P—250 μm; D, H, I, M, Q, R—100 μm; E, N, O—20 μm; F—10 μm.