Theodoxus percarinatus (Oppenheim, 1919) 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

Theodoxus percarinatus (Oppenheim, 1919) comb. nov.

Fig. 3A-T

*1919 Neritina percarinata sp. nov. - Oppenheim: 128-129, pl. 9, fig. 7.

Material.

Sample 1: c. 500 specimens (RGM 1310838) and 1 specimen (SNSB-BSPG 2023 XII 1); sample 2: 1 specimen tentatively attributed to the species (RGM 962606), 1 specimen (RGM 962607), 1 specimen (RGM 1310797), 123 specimens (RGM 1310839), 2 fragments and fragmented opercula (RGM 1310840), 1 specimen (SNSB-BSPG 2023 XII 2); sample 3: 53 specimens (RGM 1310841).

Neotype.

Oppenheim’s type material could not be found despite considerable efforts and is presumably lost (see Material and Methods section). To ensure nomenclatural stability and link the name to a type specimen, we herewith designate a neotype. The original type locality includes two localities, Giralan near Pamukkale and Bozalan near Buldan ("Abstieg nach Giralan.-Bosalan bei Bulladan.") in the Denizli Basin (Fig. 1 ). No material from those localities is available to us, but considering the geographic vicinity of the newly collected material as well as the distinct morphological features, there can be no doubt that our material represents the same species as the one described by Oppenheim (1919). We select as neotype the specimen illustrated on Fig. 3I-L , which comes from sample 2 (RGM 962607).

Description.

Globular neritid with short, flattened spire and up to 3.3 whorls. Characteristic keel is observed in part of the material. In well preserved, keeled specimens narrow, distinct keel develops early in ontogeny. In first whorl it aligns with suture, but as shell growth becomes slightly more abapically oriented, keel emerges more clearly and separates whorl top and whorl flank. Expression and extent of keel varies, it may appear and disappear within 0.2 whorls or range until last whorl; however, no specimen is found with keel covering entire shell. Strength of keel very variable, ranging from robust and well delimited to almost obsolete. In much of the material the keel is worn. Aperture broadly semicircular with broad, smooth callus that is weakly thickened especially in its center (see lateral views). Coloration variable, including fully black, white with dark stripes, irregular mix of dark and white, white blotches arranged in spiral bands or entirely white.

Dimensions.

6.64 × 7.76 mm (neotype, RGM 962607; Fig. 1I-L ), 10.66 × 10.51 mm (RGM 1310797; Fig. 1A-D ), 6.72 × 7.24 mm (SNSB-BSPG 2023 XII 1; Fig. 1M-P ).

Remarks.

The species has not been treated in the literature since the original description. It was neither included in the Fossilium Catalogus by Wenz (1930), perhaps because he considered this form not to be a freshwater taxon, nor was it listed by Taner (1974a, 1975). The combination with the genus Theodoxus appears for the first time in Alçiçek (2010), but without discussion. Here, we formalize the classification and re-describe the species.

The diagnostic character of this species is its name-giving thin keel at the transition between whorl top and flank, which distinguishes the species from most others. A similarly keeled species is Theodoxus carinatus (Fuchs, 1877) from the Lower Pleistocene (Calabrian) of Livonates (mainland Greece). It differs in the flattened whorl flanks, the weakly raised spire, the broader keel and the color pattern consisting of wavy axial lines.

In addition to the majority of keeled specimens of Theodoxus percarinatus , shells occur that lack the keel entirely and have a slightly more elevated spire (Fig. 3Q-T ). In terms of size, general shape, and color patterns these specimens fall well within the range of T. percarinatus . Many Theodoxus species are known to have highly variable shells ( Sands et al. 2020), which complicates a taxonomic decision about the status of these specimens. Apparent intermediate specimens occur in our material, but the worn nature of much of the material, the small numbers of specimens, and the general variability of the genus preclude confirmation whether it concerns untypically unkeeled representatives of T. percarinatus or constitute a separate, rare, and potentially new species.

Distribution.

Only known from the Denizli Basin.

Figures

Figure 1. Geographical and geological overview of the study area in SW Turkey (modified from Alcicek et al. 2015).

Figure 3. Neritidae of the Kolankaya I fauna. A-D. Theodoxus percarinatus (Oppenheim, 1919), RGM 1310797, sample 2. E-H. T. percarinatus, SNSB-BSPG 2023 XII 2, sample 2. I-L. T. percarinatus, Neotype, RGM 962607, sample 2. M-P. T. percarinatus, SNSB-BSPG 2023 XII 1, sample 1. Q-T. T. cf. percarinatus, RGM 962606, sample 2. Scale bars: 1 mm.