Falsipyrgula cf. sieversi (Boettger, 1881)

Neubauer, Thomas A. & Wesselingh, Frank P., 2023, The Early Pleistocene freshwater mollusks of the Denizli Basin (Turkey): a new long-lived lake fauna at the crossroads of Pontocaspian and Aegean-Anatolian realms, Zitteliana 97, pp. 53-88 : 53

Falsipyrgula cf. sieversi (Boettger, 1881)

Fig. 12G, H, M-R, U

cf. *1881 Hydrobia Sieversi Bttg. sp. nov. - Boettger: 246-247, pl. 9, fig. 23.

cf. 2014 Falsipyrgula sieversi (Boettger, 1881) - Vasilyan et al: 297, fig. 2k.

cf. 2016 Pyrgula (?) Prososthenia sieversi (O. Boettger, 1881) - Vinarski and Kantor: 242-243.

cf. 2018 Hydrobia sieversi O. Boettger, 1881 - Sitnikova et al.: 74, 75, fig. 4j [as Falsipyrgula in the discussion].

Material.

Sample 2: 1 specimen (RGM 962610), 1 specimen (RGM 1310376), 27 partly incomplete specimens and fragments (RGM 1310861), 1 specimen (SNSB-BSPG 2023 XII 20); sample 3: 1 specimen (RGM 1310375).

Type locality.

Bank deposits of the Araks River near Nakhichevan’ Town, Azerbaijan (approximately 39°10'30"N, 45°21'41"E); extant.

Description.

Small, ovoid hydrobiid with 5 whorls. Protoconch consists of ~1 whorl, without discernible sculpture but clear P/T boundary (Fig. 12U ). First teleoconch whorl smooth, soon weak, beaded keel with round, equally spaced nodules appears slightly below whorl center. Nodules increase slightly in intensity throughout ontogeny and form keel-like appearance on last whorl. Whorl profile weakly convex above nodules, convex below them, grading into weakly convex base. Last whorl attains ~70-76% (n = 3) of total shell height. Aperture ovoid, strongly inclined, faintly detached, leaving narrow umbilicus. Peristome continuous, not thickened or expanded, but weakly intensified abapical growth in final ontogeny typical of hydrobiids exposes shell layers at adapical tip.

Dimensions.

4.66 × 2.97 mm (RGM 962610; Fig. 12M-O, U ), 3.54 × 2.43 mm (RGM 1310376; Fig. 12G, H ), 3.60 × 2.56 mm (SNSB-BSPG 2023 XII 20; Fig. 12P-R ).

Remarks.

The available material shows high similarities and is perhaps conspecific with the extant Falsipyrgula sieversi (Boettger, 1881) from the Aras river in Nakhchivan (Azerbaijan). Sitnikova et al. (2018) recently studied and illustrated the holotype, which matches our specimens in terms of shell shape, size, whorl convexity, the position of the keel, the slightly convex base, and the shape and tilt of the aperture. The only difference is that the keel is not beaded as in the Denizli specimens. However, Sitnikova et al. (2018) also reported keel-less, fossil specimens of that species, confirming the variability of this trait in the Staja - Falsipyrgula species complex. Shells reported from the Early Pleistocene of the Pasinler Basin are considerably broader, nearly conical, and bear the keel at the base of the whorl ( Vasilyan et al. 2014).

Other similar species include F. osmana (Bukowski, 1930) from the Quaternary of Burdur and Kirelia carinata Radoman, 1973b (classified as Falsipyrgula by Schütt and Yildirim 1999), both of which differs in the stronger, continuous keel and the slightly more elongate shell ( Schütt and Yildirim 1999).

Distribution.

Falsipyrgula sieversi is known living and from Quaternary strata in Nakhchivan (Azerbaijan) ( Sitnikova et al. 2018), the Early Pleistocene of Armenia ( Tesakov et al. 2019), and the Pasinler Basin ( Vasilyan et al. 2014).

Subfamily indet.

Figures

Figure 12. The Staja - Falsipyrgula species complex of the Kolankaya I fauna. A-C. Falsipyrgula? coronata sp. nov., holotype, RGM 1310837, sample 2. D-F, T. F.? coronata sp. nov., SNSB-BSPG 2023 XII 18, sample 2. G, H. Falsipyrgula cf. sieversi (Boettger, 1881), RGM 1310376, sample 2. I. F.? coronata sp. nov., SNSB-BSPG 2023 XII 19, sample 3. J-L. F.? coronata sp. nov., RGM 962611, sample 2. M-O, U. F. cf. sieversi, RGM 962610, sample 2. P-R. F. cf. sieversi, SNSB-BSPG 2023 XII 20, sample 2. S. F.? coronata sp. nov., RGM 1310377, sample 2. Scale bars: 1 mm (A-R); 100 μm (S-U).