Xestopyrguloides? sagitta, Neubauer & Wesselingh, 2023

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

Xestopyrguloides? sagitta sp. nov.

Etymology.

After the Latin Xestopyrguloides sagitta meaning “arrow”, referring to the slender, pointy shape reminding of an arrowhead (noun in apposition).

Holotype.

RGM 962616 (Fig. 10K-Q ). Babadağ river valley along the Babadağ-Sarayköy road, c. 2.4 km NW of the town of Babadağ, Denizli, Turkey; sample 2 (37°50'44.5"N, 28°52'51.3"E). Kolankaya Formation, Lower Pleistocene, Gelasian.

Paratype.

SNSB-BSPG 2023 XII 12, specimen lacking aperture and apex; from type locality and stratum.

Additional material.

1 almost complete specimens and 5 fragments (RGM 1310853), 1 apertural fragment and 1 apical fragment (SNSB-BSPG 2023 XII 13); all from sample 2.

Diagnosis.

Very slender, weakly ovoid pyrguline shell characterized by small last whorl, small aperture, narrow but distinct basal keel, and whorl convexity decreasing through ontogeny.

Description.

Shell slender, elongate, faintly ovoid, almost conical, consists of about 7 whorls. Protoconch low domed, no sculpture discernible (perhaps because of poor preservation; Fig. 10O-Q ); P/T boundary not visible. Initial teleoconch whorls are convex, but convexity decreases rapidly around 3rd to 4th whorl. Following whorls are straight-sided or nearly so, with only faint convexity remaining in center of whorls. Whorls bear thin keel directly at lower suture. Keel produces slight swelling at upper suture of following whorl where it overgrows keel. Onset of keel in ontogeny uncertain due to near full overlap; keel visible in parts on at least last four whorls, matching approximately change in convexity. Last whorl relatively small, attaining 43% of shell height. Keel there produces sharp angle toward straight-sided shallow base (~55° to shell axis). Aperture not full preserved, but appears to be narrow ovoid. Inner lip covers umbilicus. Growth lines opisthocyrt, but more distinctly in upper half of whorls.

Dimensions.

3.65 × 1.37 mm (holotype, RGM 962616; Fig. 10K-Q ).

Remarks.

Only two other Xestopyrguloides have been described so far: the type species X. neumayri (Willmann, 1981) from the Early Pleistocene of Kos Island and X.? heldreichii (Fuchs, 1877) from the Pliocene of Megara, whereas the second species is only tentatively referred to the genus ( Willmann 1981, p. 202-203, textfig. 67). Both species have elongated shells with straight whorl flanks and distinct keel close to lower suture (or sometimes directly above it). Below the keel occurs a marked constriction toward the suture, which results in a weakly spruce-like appearance. Xestopyrguloides? heldreichii has in addition a slightly thickened peristome, especially at the inner lip. The lectotype designated by Willmann (1981, p. 203; NHMW 1878 XX 28) is illustrated on Fig. 10R .

The straight-sided whorls and keel at the lower suture are also present in Xestopyrguloides sagitta sp. nov. The aperture is, however, much smaller and the base is more shallow than in the other species of that genus, which is why we only tentatively allocate the Turkish species there.

A Xestopyrguloides sp. was mentioned by Schütt and Kavusan (1984) from supposedly Miocene deposits of the area around Harmancık but not illustrated. Judging from the brief description, referring to a rather stout form with lower height and a sharp keel right above the suture, it is a different species than the one we describe herein.

The new species also reminds of representatives of the genus Falsipyrgula Radoman, 1973a, many of which have a keel near the lower suture as well ( Schütt and Yildirim 1999). The type species, Falsipyrgula pfeiferi (Weber, 1927), also shares the slender shape and the straight whorl flanks ( Radoman 1973a). On average, however, Falsipyrgula species are broader and have larger and broadly ovoid apertures.

The placement in Pyrgulinae is preliminary and based on the comparison with Pontocaspian Turricaspia and Laevicaspia , with which Xestopyrguloides? sagitta sp. nov. shares the elongate, multi-whorled shell and the flattened, often smooth or faintly ornamented protoconch ( Neubauer et al. 2018; T.A.N., pers. obs.).

Distribution.

So far only known from the Early Pleistocene of the Denizli Basin.

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).