Caspia baerii Clessin & W. Dybowski in W. Dybowski, 1887

Fig. 6

Caspia Baerii nob.—Clessin & W. Dybowski in W. Dybowski 1887: 36–37.

[Caspia] Baerii n. sp. —W. Dybowski 1888: 79, pl. 3, fig. 4a, b.

Pyrgula (Caspia) baerii (Cless. & Dyb.) — Logvinenko & Starobogatov 1969: 377, fig. 367(3).

Caspia baerii Clessin et W. Dybowski in W. Dybowski, 1888— Kantor & Sysoev 2006: 87, pl. 41, fig. K.

Caspia (Caspia) baerii Clessin & W. Dybowski in W. Dybowski, 1887 — Anistratenko et al. 2019: 40, fig. 2A–I.

Caspia baerii Clessin & Dybowski in Dybowski, 1887 — Wesselingh et al. 2019: 68.

Type material. Lectotype (ZB-M W.Dyb. 96) and 116 paralectotypes (ZB-M W.Dyb. 95-97) (designated by Anistratenko et al. 2019).

Type locality. “Kaspi-See” (Caspian Sea, without further details; Table 1, locality 26).

Other material. 41 specimens in Starobogatov’s ZIN collection labelled as “ Caspia tadjallipouri ” (an unavailable collection name), collected from the eastern part of the middle Caspian Sea (locality 7).

Description. Shell small (up to 2.05 mm in height, 0.96 mm in width), slender, elongated-ovoid to slightly cylindric, with up to five whorls. Protoconch comprises c. 1.1–1.2 whorls bearing minute wrinkles and fine spiral threads (7 in Fig. 6r) placed at irregular interspaces; final 0.1 whorls of protoconch thickened (sometimes markedly), showing no or only traces of sculpture, except irregular growth lines; transition to teleoconch abrupt, marked by growth rim and onset of growth lines. Teleoconch whorls low convex, sometimes flattened in whorl centre, sometimes producing step-like appearance. Sometimes 1 or 2 fine spiral threads appear below suture, occasionally accompanied by weak striation across whole whorl profile. Last whorl attains slightly more than half of shell height. Aperture ovoid, with weak adapical angulation, sometimes slightly expanded laterally. Umbilicus covered by inner lip. Shell surface smooth, translucent, glossy. Growth lines slightly prosocline and faintly sigmoid.

Remarks. The slender shell of Caspia baerii and the weak teleoconch striation allow distinction from all other Caspiinae. The shell morphology is variable to some extent with respect to shell elongation and the expansion of the aperture, but these differences range within intraspecific variability. In Starobogatov’s material we found the “ holotype ” and 40 “ paratypes ” of a catalogue taxon he intended to describe as “ Caspia tadjallipouri ”. The shells of “ Caspia tadjallipouri ” fit very well to the lectotype of Caspia baerii in terms of shape and sculpture and are considered conspecific herein (Fig. 6 g–j, q).

W. Dybowski (1887: 36–37) and subsequent authors (Kolesnikov 1950; Golikov & Starobogatov 1966, 1972; Logvinenko & Starobogatov 1969) mentioned one or two fine spiral keels below the suture. However, the type material only occasionally shows weak spiral threads, which typically overlap visually with the base of the previous whorl shining through the translucent shell, giving the misleading impression of a stronger keel or bulge (compare light and SEM photographs, Fig. 6e and k, f and l).

Distribution. Caspian Sea. This species was mentioned from depths between 200 and 400 m in the South Caspian Basin off Azerbaijan (Mirzoev & Alekperov 2017, who reported the species as Turricaspia baerii), but the taxonomy applied in that paper is questionable and needs re-examination. No depth data is available for the material we studied (locality 7), but according to the coordinates it is approximately 70 m. No living specimens of C. baerii have been found to date.