Turricaspia? dimidiata (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

Turricaspia? dimidiata (Eichwald, 1838) Fig. 11C-E

Turricaspia dimidiata ?*1838 Rissoa dimidiata m.; Eichwald: 156.

Turricaspia dimidiata ? 1841 Rissoa dimidiata m. - Eichwald: 258, pl. 38, figs 17a-b [wrongly given as "figs 16-17" on p. 258; see also corrigendum at the end of Eichwald’s work].

Turricaspia dimidiata ? 1853 Pal. [udina] Paludina dimidiata m. - Eichwald: 285-286.

Turricaspia dimidiata ? 1887 Micromelania dimidiata Eichw. sp. - W. Dybowski: 31 [partim].

Turricaspia dimidiata ? 1888 Micromelania dimidiata Eichw. sp. - W. Dybowski: 78, pl. 1, figs 4a-f, 5 [partim].

Turricaspia dimidiata ? 1917 Micromelania (Turricaspia) dimidiata Eichw. - B. Dybowski & Grochmalicki: 32-33, pl. 4, figs 44-47 [partim].

Turricaspia dimidiata ? 1969 Pyrgula dimidiata (Eichw.). - Logvinenko & Starobogatov: 358-359, fig. 359 (1).

Turricaspia dimidiata ? 2006 Pyrgula dimidiata (Eichwald, 1838). - Kantor & Sysoev: 99, pl. 46, fig. K.

Turricaspia dimidiata ? 2016 Pyrgula dimidiata (Eichwald, 1838). - Vinarski & Kantor: 238.

Material.

1 subadult specimen ( RGM 1309787 ) .

Type material.

Not traced.

Type locality.

"In eodem lapide calcareo, fossilis" (in the same limestone [referring to the previous species, found in Dagestan], fossil).

Dimensions.

4.29 × 1.93 mm.

Description.

Slender elongate shell with ca. 6.5 whorls preserved. Protoconch granulate, originally perhaps densely malleate. First teleoconch whorl straight-sided in profile, passing into weakly convex outline on 2nd-3rd whorl. Between 3rd and 4th whorl, broad, blunt central swelling emerges, grading into thin angulation on 5th whorl; no keel is developed. Whorl portion above swelling/angulation straight-sided, below weakly convex; directly above it, weak concavity is formed locally. Aperture ovoid, strongly adnate, leaving no umbilicus, with thin peristome. Growth lines rather distinct, with prosocline upper half and near orthocline lower half.

Discussion.

A single subadult shell containing ca. 6.5 whorls (including the protoconch) is available. Size and number of whorls as well as the centrally placed angulation correspond well to Eichwald’s (1838, 1841) description and illustration of T. dimidiata . However, the central keel is very weakly expressed in our specimen and it starts not before the fourth whorl, which is why we only tentatively attribute it to this species.

Kantor and Sysoev (2006) illustrate a much more elongate specimen with cyrtoconoid spire and more abapically placed keel; it might represent a different species. Turricaspia bakuana (Kolesnikov, 1947), likewise described from Caspian Sea, too has a central keel, but differs in the much more slender shell and consistently strong keel from the second teleoconch whorl onwards (cf. Kantor and Sysoev 2006). Turricaspia basalis (B. Dybowski & Grochmalicki, 1915) has a broader conical habitus and the keel is placed near the lower suture. The subspecies T. b. laticarinata (Logvinenko & Starobogatov, 1969) only differs from T. basalis in the thickness of the keel and is herein considered a junior synonym of the nominal species.

Distribution.

Endemic to the Caspian Sea, reported from middle and south Caspian Sea at depths between 35 and 200 m ( Logvinenko and Starobogatov 1969).

Figures

Figure 11. Pyrgulinae. A-C Turricaspia? dimidiata (Eichwald, 1838), RGM 1309787 D, E Turricaspia andrussowi (B. Dybowski & Grochmalicki, 1915), RGM 1309814.