Abeskunus brusinianus (Clessin & W. Dybowski in W. Dybowski, 1887)

Neubauer, Thomas A., Velde, Sabrina van de, Yanina, Tamara & Wesselingh, Frank P., 2018, A late Pleistocene gastropod fauna from the northern Caspian Sea with implications for Pontocaspian gastropod taxonomy, ZooKeys 770, pp. 43-103 : 43

Abeskunus brusinianus (Clessin & W. Dybowski in W. Dybowski, 1887) Fig. 16A-I

Abeskunus brusinianus *1887 Zagrabica Brusiniana nob.; W. Dybowski: 52-53.

Abeskunus brusinianus 1888 Zagrabica Brusiniana n. sp. - W. Dybowski: 79, pl. 2, fig. 7.

Abeskunus brusinianus 1952 Zagrabica brusiniana W. Dyb., 1888. - Zhadin: 235, fig. 166 [partim].

Abeskunus brusinianus 1969 Pseudamnicola [( Abeskunus )] Abeskunus brusiniana (Cless. et W. Dyb.). - Logvinenko & Starobogatov: 381, fig. 367 (15).

Abeskunus brusinianus 2006 Pseudamnicola brusiniana (Clessin et W. Dybowski in W. Dybowski, 1888). - Kantor & Sysoev: 114, pl. 51, fig. J.

Abeskunus brusinianus 2016 Pseudamnicola brusiniana (Clessin et W. Dybowski in W. Dybowski, 1888). - Vinarski & Kantor: 222.

Material.

489 specimens ( RGM 1309834 , RGM 1309842 , RGM 1310194 , LV 201505 ) .

Type material.

Not traced.

Type locality.

“Kaspi-See” (Caspian Sea, no further details mentioned).

Dimensions.

4.12 × 3.82 mm ( RGM 1309834, Fig. 16A, F ); 4.15 × 3.65 mm ( LV 201505, Fig. 16B, C, I ); 3.00 × 2.74 mm ( RGM 1309842, Fig. 16D, E, G, H ); 4.14 × 3.42 mm; 4.15 × 3.53 mm; 4.34 × 3.79 mm; 4.39 × 3.87 mm; 4.59 × 3.68 mm.

Description.

Shell broadly conical, comprising up to 4.5 whorls. Protoconch broadly domical, with almost immersed initial part; consists of 1.25 whorls, measures 525 µm in diameter; nucleus is ca. 160 µm wide; nucleus surface covered with irregular elongated wrinkles; protoconch surface wrinkled, bearing thin, irregular spiral grooves on first third, passing over irregular pattern of faint spiral grooves and wrinkles into numerous, regularly parallel spiral furrows on last third; P/T transition without growth rim, marked by onset of growth lines. Teleoconch whorls highly convex, with maximum convexity in adapical half, producing slightly stepped spire. Last whorl attains 77-85% of shell height. Aperture drop-shaped, slightly inclined, with marked adapical notch at contact to penultimate whorl. Outer peristome margin not or slightly thickened, columellar and parietal margins weakly thickened; peristome slightly expanded towards columella (protruding towards umbilicus in lateral view) and strongly towards base; weakly sinuate in lateral view, with broad but weak adapical protrusion and straight-sided abapical part. Umbilicus narrow, slit-like. Prosocline growth lines cover shell surface.

Discussion.

The species differs from the type species A. exiguus (Eichwald, 1838) in the conical shell, the taller spire, the less inflated last whorl, and the distinct umbilicus. Abeskunus brusinianus michelae Tadjalli-Pour, 1977 is much more globular than A. brusinianus . The latter species strongly reminds of and might be conspecific with A. exiguus . Pseudamnicola depressispira Logvinenko & Starobogatov, 1969, which these authors also included in the subgenus Abeskunus , differs from the presumed congeners in the valvatoid shape with very wide umbilicus and small but distinct riblets.

Pseudamnicola? brusiniana Pavlović, 1903 is a junior secondary homonym of this species, for which Neubauer et al. (2015b) introduced Pseudamnicola? babindolensis as replacement name. Because of the revised classification, P.? brusinianus [sic] Pavlović is reinstated as valid, with P.? babindolensis as its junior objective synonym ( ICZN 1999, Art. 59.4).

Distribution.

Endemic to the Caspian Sea, in the southern and middle part at a depth of> 250 m ( Logvinenko and Starobogatov 1969, Parr et al. 2007).

Figures

Figure 16. Hydrobiidae incertae sedis. A, F Abeskunus brusinianus (Clessin & W. Dybowski in W. Dybowski, 1887), RGM 1309834 B, C, I A. brusinianus, LV 201505 D, E, G, H A. brusinianus, RGM 1309842.