Dreissena kairanderensis (Oppenheim, 1919)

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

Dreissena kairanderensis (Oppenheim, 1919)

Fig. 17A-J

*1919 Congeria (?) Dreissena kairanderensis sp. nov. - Oppenheim: 126-127, pl. 6, fig. 11.

? 1919 Dreissensia (?) Dreissena phrygica sp. nov. - Oppenheim: 124-125, pl. 6, figs 1-3.

? 1919 Dreissensia (?) Prososthenia hierapolitana sp. nov. - Oppenheim: 127-128, pl. 6, fig. 12.

Material.

Sample 2: 5 valves (RGM 962698-962702), c. 690 valves (RGM 1310845), 2 valves (SNSB-BSPG 2023 XII 23); sample 3: 28 valves (RGM 1310846).

Type locality.

"Kairandere zwischen Bosalan und Bulladan" [Kairandere between Bozalan and Buldan], Denizli Basin, Turkey.

Description.

Variably shaped Dreissena with outlines ranging from mytiliform to flat, wide, and broad with apparent intermediate shapes. Dorsal margin usually curved but in some specimens can be straight. Ventral margin slightly curved, lacks byssate inflection. Semidiameter located toward ventral margin in adult stages. External ornamentation remarkably variable. Most specimens contain some sort of fanning out (axial) ribs. Number, shape, and length of these ribs highly variable; smooth specimens also occur. Typically 1-3 ribs develop almost immediately below umbo; often most prominent rib located at dorsal margin forms distinct dorsal angle. Ribs can fade within short distance or run entire shell length. Irregular small secondary ribs occur in some specimens. Hinge plate variable in strength. Plane of symmetry appears to be flat.

Dimensions.

All material is broken, but measurements from cracked specimens in the field gave maximum dimensions of approximately 25 × 21 × 9.5 mm (width × height × semidiameter) for adult valves.

Remarks.

Our material concerns a hugely variably shaped species for which additional study is required to determine whether it is a single species or consists of multiple species. Our juvenile and broken adult material does not enable making such a distinction. The flat plane of symmetry, the lack of a byssate inflexion on the shells exterior, and the relative prominence of the posterodorsal ridge in many of the specimens makes a close relationship with the Dreissena polymorpha Pallas, 1771 species group possible.

The species differs from the co-occurring Dreissena sp. 1 particularly in the shifting position of the semidiameter through ontogeny, which runs with an almost straight line 45° from the umbo toward the posterior margin, and the generally more curved shell. Dreissena phrygica Oppenheim, 1919 and D. hierapolitana Oppenheim, 1919, both also described from the Denizli Basin, seem to differ from Dreissena kairanderensis mostly in size, shell curvature, and/or the presence of additional keels. Given the variability we observe in our material, these names probably only signify morphological varieties of a single, polymorphic species. However, further studies are required to verify their taxonomic status. The same applies to other Denizli dreissenids, i.e., Dreissena lycophila Oppenheim, 1919, Dreissena filifera Andrusov, 1893, sensu Taner, 1974b, Congeria prekairenderensis Taner, 1974b, and C. spathulata minor Taner, 1974b [non Congeria minor Fuchs, 1877], all of which require investigation.

Distribution.

Endemic to the Denizli Basin.

Figures

Figure 17. Dreissenidae of the Kolankaya I fauna. A, B. Dreissena kairanderensis (Oppenheim, 1919), RGM 962699, sample 2. C, D. D. kairanderensis, RGM 962701, sample 2. E, F. D. kairanderensis, RGM 962702, sample 2. G, H. D. kairanderensis, RGM 962700, sample 2. I, J. D. kairanderensis, RGM 962698, sample 2. K, L. Dreissena sp. 1, RGM 962703, sample 2. M, N. Dreissena sp. 1, RGM 962704, sample 2. Scale bar: 2 mm.