Iraklimelania minutissima, 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

Iraklimelania minutissima sp. nov.

Etymology.

Referring to the exceptionally small shell size.

Holotype.

RGM 962617 (Fig. 7A-E ). 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.

Additional material.

One juvenile or subadult form (SNSB-BSPG 2023 XII 5; Fig. 7F-J ) from sample 2.

Diagnosis.

Very small, slender hydrobiid with highly convex and slowly growing whorls that show weak subsutural concavity in late ontogeny, small aperture with weak bulge at columella, and sigmoidal growth lines.

Description.

Exceptionally small, slender hydrobiid shell, with slightly less than 5 whorls that slowly expand in width and height. Protoconch consisting of c. 1.2 whorls; low domed with broad nucleus, malleate surface, with initially tiny mesh-size, which becomes coarser toward P/T transition; P/T transition indicated by growth stop and onset of growth lines. Whorls highly convex throughout ontogeny; in last two whorls, faint concavity forms below suture. Last whorl attains c. 53% of total shell height. Base ~45°, straight-sided. Aperture small, elliptical; weak bulge occurs at columella. Inner lip covers sheet-like base of penultimate whorl, slightly expanded across columella, leaving very narrow umbilicus; outer lip not preserved. Growth lines distinct, sigmoidal, with opisthocyrt upper half and prosocyrt lower half.

Dimensions.

1.93 × 0.83 mm (holotype, RGM 962618; Fig. 7A-E ).

Remarks.

We attribute the new species to the genus Iraklimelania based on the following characters matching the type species, I. levis Willmann, 1981, from the Lower Pleistocene Irakli Formation of Kos Island: the small size; the small, simple aperture, having a slight bulge at the columella; the highly convex whorls, characterized by a narrow, faint constriction below the suture ("weak, concave sulcus" of Willmann 1981); the sigmoidal growth lines; the faint spiral striae. Our species can be distinguished by the even smaller size, the exceptionally slender shape and the narrower subsutural constriction. The only other species known for that genus,? Iraklimelania coa Willmann, 1981 from the Lower Pleistocene Tafi Formation of Kos, differs in the conical shell and the presence of a blunt keel near the lower suture.

In addition to the holotype, a juvenile or subadult specimen is considered to belong to the new species (Fig. 7F-J ). In that shell, the sigmoidality of the growth lines is not yet fully expressed, but the other features fit well to the holotype.

Distribution.

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

Figures

Figure 7. Caspiinae (Hydrobiidae) of the Kolankaya I fauna. A-E. Iraklimelania minutissima sp. nov., holotype, RGM 962618, sample 2. F-J. Iraklimelania minutissima sp. nov., juvenile or subadult form, SNSB-BSPG 2023 XII 5, sample 2. K-P. Iraklimelania submediocarinata sp. nov., holotype, RGM 962689, sample 1. Scale bars: 1 mm (A-D, F-I, K-N); 100 μm (E, J, O, P).