Schapsugia pulcherrima ( Starobogatov, 1962 ) 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 : 266-267

Schapsugia pulcherrima ( Starobogatov, 1962) , comb. n.

( Fig. 5 , 6A–J ; Tables 2, 4)

Paladilhiopsis pulcherrima Starobogatov, 1962: 46 , fig. 2 (А–Б); Vinarski & Kantor, 2016: 218; Sitnikova et al., 2017: 282, fig. 10, G–H.; Grego et al., 2020: 35

Paladilhiopsis orientalis Starobogatov, 1962: 46-47 , fig. 2 (Д); Vinarski & Kantor, 2016: 217–218; Sitnikova et al., 2017: 281- 282, fig. 10, D–F; Grego et al., 2020: 35.

Paladilhiopsis subovata Starobogatov, 1962: 46 , fig. 2 (Е); Vinarski & Kantor, 2016: 218; Sitnikova et al., 2017: 282, fig. 10, K–L; Grego et al., 2020: 35

Description. Shell small (SH <2.65 mm), fragile, turriculate, or high-conical. Whorls rounded and strongly convex, separated by a deep suture. Whorl number up to 6.0 (5.25 on average). Spire high, usually exceeds 0.60 SH. Body whorl high and oblong, constitutes about 0.60 SH. Aperture triangular-ovoid, narrowed in its upper part, with relatively thickened inner peristome, whose parietal margin can lean against body whorl. Outer lip bent outward. Umbilicus very narrow, slit-like ( Fig. 5 , 6A–B ). Protoconch broad (up to 370 μm in diameter), low domed-shaped, typically consisting of 1.5 whorls. Initial part of embryonic shell reaches 205 μm in diameter. Protoconch separated from teleoconch by a not always clearly distinct axial line. Several axial growth lines often appear at the border of the embryonic shell ( Fig. 6I ).

Operculum ovoid, corneous, thin, paucispiral with submarginal nucleus, generally orange or yellowish. Outer surface flat with axial growth lines. Nucleus area on the inner side thickened and raised into hook-like peg ( Fig. 6C ). Radula: Two basal cusps on each side of rachis and four cusps on each side of median cusp of rachis. Median cusp only slightly longer than adjacent ones, all cusps relatively long and narrow. On lateral tooth, there are four cusps on each side of the largest cusp, all cusps long and narrow like those of rachis. Inner marginal tooth with 20 cusps, outer marginal tooth with 18 cusps ( Fig. 6E ).

Penis with small warty-shaped lobe on pike-shaped distal part. Proximal part of penis slightly tapered compared to distal part. Distal part bears a fin-like edging consisting of thin and relatively fragile cells. Tip narrowed, with curved papilla ( Fig. 6F–H ).

Holotype. Absent from ZIN collection, probably lost (see Sitnikova et al., 2017 for details). Shell dimensions of the holotype at five whorls, mm (after Starobogatov, 1962): SH 1.85; SW 0.90; AH 0.90; AW 0.50.

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.

Habitat and distribution. Endemic of Krasnodar Krai, known from Krasnoaleksandrovskaya and Tigrovaya Caves ( Fig. 1D, C ). Inhabits subterranean brooks. Mollusks occur on solid substrates, especially submerged stones; population density is low, snails are rare, and live only in the depths of the cave though dry shells are abundant in the cave brook sediments.

Variation. A variable species, both in shell shape and proportions within Krasnoaleksandrovskaya Cave’s population (see Tables 2, 3; Fig. 5 ). Figure 5 visualizes the conchological diversity in this sample. Please note that Fig. 5 illustrates the most divergent specimens from Krasnoaleksandrovskaya Cave. One can find shells with “intermediate” characters in this cave that form a full continuous series of variations, and the most different individuals of this sample are connected by gradations. Specimens of this species from Tigrovaya Cave ( Fig. 1D ) differ by having lower and broader shells with a wider protoconch. These differences, albeit small, allow us to hypothesize that the Tigrovaya Cave population represents a distinct species, but the available information is not enough to check this assumption.

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 5. The conchological disparity and variety of ‘Paladilhiopsis’ specimens collected in Krasnoaleksandrovskaya Cave. Scale bar: 500 μm.

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.