Prososthenia cf. sturanyi communis Willmann, 1981

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

Prososthenia cf. sturanyi communis Willmann, 1981

Fig. 10A-J

cf. 1981 Prososthenia sturanyi communis ssp. nov. - Willmann: 160, pl. 6, figs 10, 11 (cum syn.).

Material.

1 specimen (RGM 962615), 7 specimens, 2 apertural fragments, and 2 apical fragments (RGM 1310852), 1 specimen (SNSB-BSPG 2023 XII 11); all from sample 2.

Type locality.

Valley between Vokasia and Sefto valley, c. 3.5 km SW of Kos, Kos Island, Greece; lower Kos Formation, Lower Pleistocene.

Description.

Shell elongate, ovoid, with 5 whorls that decrease in convexity. Early whorls regularly convex; penultimate to last whorl weakly convex to flattened in whorl center; last whorl occasionally has faint concavity below faintly expressed subsutural bulge; suture moderately incised. Base weakly convex to straight-sided. Aperture typically drop-shaped, relatively broad, only weakly inclined; slightly offset in fully grown specimen; peristome weakly and equally thickened, faintly expanded; umbilicus very narrow. Growth lines rather weak, weakly prosocline in upper half to nearly orthocline in lower half, crossed by faint spiral furrows. Protoconch consisting of ~0.9 whorls, with broad nucleus, covered by fine-meshed malleate sculpture.

Dimensions.

2.86 × 1.33 mm (RGM 962615; Fig. 10A-E ), 2.77 × 1.20 mm (SNSB-BSPG 2023 XII 11; Fig. 10F-J ).

Remarks.

Prososthenia sturanyi encompasses shells with highly variable shapes and sizes ( Willmann 1981). Slender specimens of P. s. communis from Kos Island match the Denizli material in terms of general shape, the flattened whorl flanks, the presence of a weak subsutural band, and faint spiral furrows, as well as the shape of the aperture (compare Willmann 1981, pl. 6, fig. 11). Yet, the Kos specimens are slightly larger and the apex appears to be smaller. Considering the otherwise close similarity, the generally great variability of the species, and the similar age and geographic vicinity, we tentatively refer the Denizli material to Prososthenia sturanyi communis .

Prososthenia sturanyi sturanyi (Bukowski, 1896) from Plio-Pleistocene formations of Rhodes has a stouter shell with a shorter spire ( Willmann 1981). Prososthenia gregaria (Fuchs, 1877) from the Early Pleistocene of mainland Greece is much larger and has a slender, elongate shell with regularly, low-convex whorls. A particularly similar species is Prososthenia eburnea Brusina, 1897 from Middle Miocene (Langhian) strata of Miočić, Croatia, regarding the decreasing degree of whorl convexity through ontogeny. The species is, however, much larger and more regularly ovoid. The malleate protoconch (Fig. 10E ), prosocline-orthocline growth lines, and the presence of spiral furrows also agree with a placement in the genus Prososthenia (compare Neubauer et al. 2020).

The taxon is also surprisingly similar to " Caspia " Prososthenia laevigata Jekelius, 1944 (p. 123-124, pl. 45, figs 9, 10) from the Early Pannonian (Early Tortonian) of Soceni in Romania. That species has a similarly slender, ovoid shell with straight-sided whorls, an angulation on the last whorl toward the straight base, and a slender ovoid aperture. It differs in the early whorls being also nearly straight-sided, where the Denizli species has convex whorls. Furthermore, there seems to be no umbilicus in the Romanian species. On a side note, despite the superficial similarity, it is questionable whether that species is a member of the genus Caspia and the Caspiinae . Shells of that group are characterized by a broad and rounded, dome-like protoconch. The Romanian species rather suggests a placement in Pyrgulinae , perhaps even Prososthenia . If, however, the species was transferred to Prososthenia , the species name Prososthenia laevigata Volkova, 1953 would be become a secondary homonym.

Distribution.

Late Pliocene to Early Pleistocene (Phoka, Sefto, and Kos formations) of Kos Island ( Willmann 1981) and, tentatively, Early Pleistocene of the Denizli Basin (this study).

Figures

Figure 10. Pyrgulinae (Hydrobiidae) of the Kolankaya I fauna. A-E. Prososthenia cf. Prososthenia sturanyi Prososthenia communis Willmann, 1981, RGM 962615, sample 2. F-J. P. cf. Prososthenia sturanyi Prososthenia communis, SNSB-BSPG 2023 XII 11, sample 2. K-Q. Xestopyrguloides? sagitta sp. nov., holotype, RGM 962616, sample 2. R. Xestopyrguloides? heldreichii (Fuchs, 1870), lectotype (designated by Willmann 1981), NHMW 1878 XX 28, Megara, Pliocene. S-U. Xestopyrguloides? sp., RGM 1365347, sample 2. Scale bars: 1 mm (A-D, F-I, K-N, R-T); 100 μm (E, J, O-Q).