Valvata koehleri, Harzhauser & Neubauer & Hoşgör, 2018

Harzhauser, Mathias, Neubauer, Thomas A. & Hoşgör, İzzet, 2018, Oligocene-Miocene freshwater gastropods from the Oltu-Narman Basin in eastern Turkey, Acta Palaeontologica Polonica 63 (2), pp. 357-369 : 362-364

Valvata koehleri sp. nov.

Fig. 4 .

ZooBank LSID: urn:lsid:zoobank.org:act:A0E6BDE6-C921-46D7-B7AA-3CA72DD43C88

Etymology: Referring to Frank Köhler (Australian Museum Sydney), in honour of his contributions to malacology.

Type material: Holotype: NHMW 2018 /0019/0015, moderately preserved, fully grown specimen ( Fig. 4D ) . Paratypes: NHMW 2018 / 0019/0016, compressed, adult specimen ( Fig. 4B ) ; NHMW 2018 / 0019/0017, slightly compressed, adult specimen ( Fig. 4C ) ; NHMW 2018 /0019/0018, compressed, adult specimen ( Fig. 4A ) ; NHMW 2018 /0019/0019, laterally compressed specimen. All from type locality and horizon .

Type locality: Kömürlü (40°46’14.74” N, 42°18’21.05” E, WGS84 ), Oltu-Narman Basin , northeastern Turkey .

Type horizon: Marly silt and sand of the upper Susuz Formation; upper Oligocene or lower Miocene.

Material.— Type material only.

Diagnosis.—Small robust shell characterized by extraordinarily blunt and protruding axial ribs and strongly changing outline of teleoconch whorls during ontogeny from gradate conical to moderately high conical. Protoconch conical, comprising 1.3 strongly convex whorls with incised suture. Early teleoconch whorls with distinct angulation and orthocline axial ribs. Second and third teleoconch whorls rapidly widening with angulation at lower suture; fourth teleoconch whorl comparatively narrow but distinctly increasing in height. Suture deeply incised. Blunt axial ribs continue on base up to strongly reduced umbilicus. Inner lip distinct, reflected; outer lip coinciding with axial rib.

Description.—Small, very robust shells with strongly allometric growth ( Table 3). Conical protoconch of 950 μm diameter and 550 μm height, comprising 1.3 strongly convex whorls with incised suture. Transition into teleoconch indistinct, indicated by onset of weak axial ribs. First teleoconch whorl strongly angulated with nearly flat sutural ramp and straight flank. Weak axial riblets, bearing tiny nodes at angulation, on early whorls pass into successively more prominent orthocline axial ribs increasing in width. Cross-section of ribs changing successively from convex to trigonal. Axial ribs become blunt and wide-spaced within second teleoconch whorl; angulation shifts slightly downwards resulting in steeper sutural ramp; flank of whorl becomes more conical, with maximum diameter at lower suture. Axial ribs now distinctly recessed close to lower suture, coinciding with slight angulation. Third teleoconch whorl strongly widening, broad conical; axial ribs becoming strongly prosocline and extremely blunt, being reminiscent of spines in apical view (axial ribs account for about 1/3 of diameter at that stage); ribs partly laterally dented, forming shallow, irregular concavities. Transition into weakly convex base of third teleoconch whorl strongly accentuated by lower angulation. Fourth teleoconch whorl less expanding but increasing in height; upper and lower angulation weakening towards aperture; blunt, prosocline to slightly sigmoidal axial ribs becoming less protruding on last whorl. Aperture only partly preserved; distinct inner lip well demarcated from base; axial ribs continue on weakly convex base; umbilicus reduced to narrow chink, largely covered by reflected inner lip. Outer lip coincides with varix-like axial rib terminating in thin peristome (destroyed during preparation).

Remarks.—This species is characterized by a striking allometry in whorl shape and sculpture. Especially the height of the third teleoconch whorl is variable, ranging from depressed ( Fig. 4B ) to moderately high ( Fig. 4D ). Only few valvatids with axial sculpture have been described from the Miocene and Pliocene of the eastern Mediterranean region. Of these, Valvata cincta Taner, 1974a , as described by Wesselingh et al. (2008) from the late Miocene of Turkey, has prominent axial ribs too but differs in the higher spire, more numerous and less blunt axial lips and the presence of an umbilicus. Similarly, the axial ribs of Valvata pagana Bulić and Jurišić- Polšak, 2009, from the middle Miocene of Pag Island ( Croatia), are less prominent and more numerous, and the species develops a moderately wide and deep umbilicus. Among Recent valvatids, the Greek Valvata klemmi Schütt, 1962 is highly reminiscent of the Turkish fossil in respect to the strongly angulated whorls and the persisting axial ribs on the base. It differs in the much weaker axial ribs and the broader umbilical chink. This extant species was placed by Schütt (1962) in Costovalvata Poliński, 1929 , with the type species Valvata Costovalvata ) hirsutecoststa Poliński, 1929. Similarly, Bulić and Jurišić- Polšak (2009) placed their Miocene V. pagana with question mark in the subgenus Costovalvata . Valvata Costovalvata ) hirsutecoststa is endemic to Lake Ohrid, has a typical valvatid shell and is characterized by a cancellate sculpture in which spiral cords are nearly as prominent as the axial ribs. The morphology and type of sculpture have little in common with V. pagana and V. klemmi . Therefore, we doubt a closer relationship. A potential genus name for these species would be Aegaea Oppenheim, 1891 , which was introduced by Oppenheim (1981) for Valvata vivipariformis Oppenheim, 1891 from the Pleistocene of Kumari near Aegion ( Greece). Oppenheim (1891) based the genus on the presence of prominent axial ribs and the narrow to nearly closed umbilicus, which is untypical for Valvata . As pointed out by Haszprunar 2014), however, the angulated aperture of Valvata vivipariformis rather suggests a relation with viviparids, rendering Aegaea a problematic taxon.

The excessive sculpture of V. koehleri is reminiscent of some Melanopsidae as described by Neubauer et al. (2013) from the middle Miocene of the Dinaride Lake System. Protoconch morphology and shape of the aperture exclude a relation with that family. Cretaceous to Paleocene Stomatopsidae Stache, 1889 are superficially similar concerning the prominent axial ribs but differ clearly by their elongate shells, their much larger size and the strongly callous inner lip (see Stache 1889).

Figures

Fig. 4. Valvatid gastropod Valvata koehleri sp. nov. from the upper Oligocene–lower Miocene Susuz Formation, Kömürlü, Turkey. A. NHMW 2018/0019/0018, paratype in apertural (A1), lateral (A2), apical (A3), and umbilical (A4) views. B. NHMW 2018/0019/0016, paratype in lateral (B1, B2), apical (B3), and umbilical (B4) views. C. NHMW 2018/0019/0017, paratype in lateral views (C1, C2); protoconch (C3). D. NHMW 2018/0019/0015, holotype in apical (D1), umbilical (D2), apertural (D3), lateral (D4), and dorsal (D5) views. Scale bars 2 mm, if not stated otherwise.