Clessiniola variabilis (Eichwald, 1838)

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

Clessiniola variabilis (Eichwald, 1838) Fig. 7A-I

Clessiniola variabilis *1838 Paludina variabilis m.; Eichwald: 151-152.

Clessiniola variabilis 1841 Paludina variabilis m. - Eichwald: 253-254, pl. 38, figs 6-7.

Clessiniola variabilis 1853 Pal. [udina] variabilis m. - Eichwald: 285.

Clessiniola variabilis 1887 Clessinia variabilis Eichw. sp. - W. Dybowski: 41-42.

Clessiniola variabilis 1888 [ Clessinia ] Clessinia variabilis Eichw. sp. - W. Dybowski: 79, pl. 2, fig. 6.

Clessiniola variabilis 1952 Clessiniola variabilis (Eichwald, 1841). - Zhadin: 255, fig. 199.

Clessiniola variabilis 1966 P. [yrgula] (Clessiniola) variabilis. - Golikov & Starobogatov: 356, fig. 2 (2).

Clessiniola variabilis 1969 Pyrgula [( Clessiniola )] Clessiniola variabilis (Eichw.) - Logvinenko & Starobogatov: 377, fig. 367 (1).

Clessiniola variabilis 1987 T. [urricaspia] variabilis (Eichw.). - Alexenko & Starobogatov: 34, fig. 5.

Clessiniola variabilis 2006 Turricaspia variabilis (Eichwald, 1838). - Kantor & Sysoev: 111, pl. 49, fig. J.

Clessiniola variabilis 2011 Turricaspia variabilis (Eichwald, 1838). - Anistratenko et al.: 85, fig. 3 (15).

Clessiniola variabilis 2014 Turricaspia variabilis . - Taviani et al.: 4, fig. 3b.

Clessiniola variabilis 2016 Turricaspia variabilis (Eichwald, 1838). - Vinarski & Kantor: 251.

Material.

4867 specimens ( RGM 1309815 , RGM 1309826 , RGM 1309827 , RGM 1309831 , RGM 1310243 -1310247, LV 201507 ) .

Type material.

Not traced.

Type locality.

"In Volgae ostio prope Astrachanum, et versus mare Caspium; etiam fossili in calcatio lapide conglutinato recentissimo Dagesthanici littoris" (at the Volga river mouth near Astrakhan, and towards the Caspian Sea; also in recently lithified fossil limestone at the shores of Dagestan).

Dimensions.

5.91 × 3.31 mm ( LV 201507, Fig. 7A-C ); 6.31 × 3.59 mm ( RGM 1310246, Fig. 7D ); 4.60 × 2.35 mm ( RGM 1310245, Fig. 7E ); 6.08 × 3.18 mm ( RGM 1310243, Fig. 7F-H ); 6.85 × 3.89 mm ( RGM 1310244).

Description.

Broadly drop-shaped to rarely conical shell of up to six whorls. Protoconch insufficiently preserved to specify extent and surface sculpture; P/T transition indistinct; first whorl measures ca. 340 µm in diameter. Teleoconch whorls moderately and regularly convex; sometimes, spire is very faintly stepped; suture narrow. In many specimens, shells starts to grow stronger in abapical direction in course of last (two) whorl(s), producing non-parallel suture and relatively higher penultimate whorl. Rarely, forms with comparatively slender shape and regularly increasing whorls (and thus relatively smaller last and penultimate whorls) occur. Both types are linked via intermediates. Aperture regularly ovoid, inclined; inner lip glossy, weakly to sometimes more prominently thickened; strongly adnate, sheet-like expanded over base of penultimate whorl and columella, rarely leaving very narrow umbilicus; broad, shallow spout occurs at transition between columella and base; outer lip mainly thin, sometimes weakly thickened at anterior notch. Growth lines very faint, with prosocline upper third and near orthocline lower two-thirds.

Discussion.

This species displays a large morphological variability within our ample material. Shell shape ranges between slender conical to broadly ovoid, sometimes with weakly irregular growth. Likewise, shell size, whorl convexity, and number of whorls vary considerably. Yet, these features intergrade without clear boundary, rendering a distinction of species unreasonable.

The morphological variability is not restricted to our material but a general feature of Clessiniola . It was documented by several previous authors, partly for specimens from the same localities (e.g., Eichwald 1838, Issel 1865, W. Dybowski 1887-1888, Golikov and Starobogatov 1966, Logvinenko and Starobogatov 1969, Alexenko and Starobogatov 1987, Anistratenko et al. 2011). The species concepts applied by the different authors, however, varied greatly. The present material includes shells that have been variably attributed to the species C. variabilis (Eichwald, 1838), C. triton (Eichwald, 1838) and C. martensii (Clessin & W. Dybowski in W. Dybowski, 1887). The Clessiniola triton -morphotype sensu Eichwald characterizes broad specimens with slightly detached aperture (see also Kantor and Sysoev 2006); these forms are rarely represented in our material. Eichwald (1838, 1841) himself confirmed the rarity of the form, also stating that he did not find a living representative (in contrast to C. variabilis ). The Clessiniola martensii -morphotype was introduced for similarly broad morphologies. (Note that Clessin and W. Dybowski used a different concept of C. triton , there having a rather elongate conical shell.)

Because of the fluent morphological transition between forms traditionally referred to as C. variabilis , C. triton and C. martensii , as well as their joint occurrence in several localities in the Pontocaspian region, one might consider all of them synonymous. Personal observations on Holocene material from Dagestan area, however, indicate indeed distinguishable morphotypes without intermediates. Moreover, frequent shell repair found in most of the Selitrennoye specimens additionally complicates an unbiased view on morphological diversity. A more in-depth investigation comparing undamaged material from different sites is thus required.

Given the large variability, the Caspian species Clessiniola ovum (Logvinenko & Starobogatov, 1969) and C. trivialis (Logvinenko & Starobogatov, 1969), as well as C. pseudotriton (Golikov & Starobogatov, 1966) from the Dniester River mouth (compare Kantor and Sysoev 2006), might too be considered as synonyms of C. variabilis . However, the original descriptions and drawings provided impede clarification of their statuses.

Clessinia ahngeri Westerlund, 1902 is often listed as junior synonym of C. variabilis , but without discussion (e.g., Logvinenko and Starobogatov 1969, Vinarski and Kantor 2016). The original description of C. ahngeri suggests close similarities indeed between both species claiming, however, that it differs from other congeners in the much larger spire (11 × 5 mm) and the slightly sinuate outer lip. Examination of Westerlund’s (1902b) material is required to ascertain the alleged synonymy.

The record of " Paludina Eichwaldi Kryn." Eichwald (1841) listed in synonymy of C. variabilis refers to a nomen nudum mentioned in a species list by Krynicki (1837).

Distribution.

Endemic to the Pontocaspian region. Found in the Caspian Sea and the lower courses of rivers and freshwater parts of the Azov and Black seas ( Anistratenko et al. 2011, Vinarski and Kantor 2016). Also reported from Neoeuxinian (late Pleistocene) deposits of the Marmara Sea ( Taviani et al. 2014).

Figures

Figure 7. Pyrgulinae. A-C Clessiniola variabilis (Eichwald, 1838), LV 201507, broad morphotype D C. variabilis, RGM 1310246, broad morphotype E C. variabilis, RGM 1310245, slender morphotype F-H C. variabilis, RGM 1310243, slender morphotype I C. variabilis, RGM 1309827.