Viviparus cf. maeoticus (Bogachev and Shishkina, 1919)

Frolov, Pavel D., Danukalova, Guzel A. & Osipova, Eugenia M., 2018, Late Miocene molluscs of the Morskaya 2 site (Azov Sea region, Russia), Palaeontologia Electronica (a 20) 23 (1), pp. 1-32 : 12

Viviparus cf. maeoticus (Bogachev and Shishkina, 1919)

Figure 5.5

1919 Paludina maeotica Bogachev and Shishkina , p. 38-39.

Material. 692 specimens from layer 3.

Description. The shell is oval-conical with a blunted spire (HS is 6.2-14.2 mm, average 7.8; WS is 6.2-12 mm, average 7.5), moderately high (WS/ HS is 0.84-1.0, average 0.9), consisting of 5-6 convex whorls, and separated by a moderately deep suture. Spire is short, pointed. The last whorl is rounded and slightly bended to the suture, about 3/ 4 or more of the shell height (HLW/HS is 0.8-0.9, average 0.85). Aperture has an ovoid form, pointed in the upper part (WA/HA is 0.8-1.1, average 1.0); it is about 2/3 of the total shell height (HA/HS is 0.6- 0.7; 0.61). Aperture edges are thin, not thickened. Umbilicus is slit-like, covered by the inner edge. The shell surface is covered by fine hatching. Opercula are not found.

Remarks. This species is very close to Viviparus achatinoides (Deshayes, 1838) .

Variability. The form is characterised by high variability in shell size and height-to-width ratio due to sexual dimorphism. Young specimens differ from adult forms in a more rounded and lower shell. Shells of adult forms are more elongated and taller. Region of distribution and age. Late Miocene of the the northeastern Azov Sea region.

Figures

FIGURE 5. Assemblage of the Maeotian freshwater molluscs (layer 3). 1, Borysthenia cf. pronaticina (Lindholm, 1932). 2-3, Lithoglyphus acutus Cobălcescu, 1883; 2, smooth shell; 3, shell with keel. 4, Viviparus cf. karaganicus Volkova, 1939. 5, Viviparus cf. maeoticus (Bogachev and Shishkina, 1919). 6, Lymnaea sp. 7, Sphaerium rivicola Lamarck, 1818. 8, Gyraulus cf. acronicus (Ferrussac, 1807). 9-10, Bithyniidae, opercula.