Borysthenia cf. pronaticina (Lindholm, 1932)

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 : 15

Borysthenia cf. pronaticina (Lindholm, 1932)

Figure 5.1

1932 Valvata (Borysthenia) pronaticina Lindholm , p. 17-18, pl. 3, fig. 8 a-h.

1983 Valvata pronaticina Lindholm ; Chepalyga,

Sidnev, p. 63-64, pl., 2, figs. 1-3.

2007 Valvata pronaticina Lindholm ; Sanko, p.

78, drawing 58/4.

Material. 3 specimens from layer 3.

Description. Oval-conical shell, with a pointed spire (HS is 4.4-6.5 mm, average 5.2; WS is 4.8- 6.6 mm, average 5.4), medium height (WS/HS is 1.0-1.1, average 1.03), consists of 4-4.5 rounded whorls separated by a deep, slightly sloping suture. Protoconch consists of 1,5 whorls. Whorls of the spire are slightly swollen and they grow slowly. The last whorl prevails over the others, strongly inflated (HLW/HS is 0.9). Aperture has an ovate form, large, pointed in the upper part (WA/HA is 0.8-0.9, average 0,85), is about 1/2 of the total shell height (HA/HS is 0.6). The outer edge of aperture is thin. Umbilicus is open slit-shaped. A thin uneven radial hatching covers shell surface.

Remarks. There are three specimens in our collection, which we attribute to Borysthenia . Morphologically, these specimens demonstrate close similarity to the species Borysthenia pronaticina (Lindholm, 1932) and Borysthenia goldfussiana (Wüst, 1901) .

Valvatidae specimens from the Morskaya 2 site differ by their smaller spires from typical Borysthenia pronaticina illustrated by Lindholm (1932, pl. 3, fig. 8a-h). Our specimens are most similar to B. pronaticina from the Strelitza quarry (Early Middle Pleistocene of the upper Don area) (Sanko, 2007, p. 78, fig. 58/4). In general, shells of Borysthenia from Morskaya 2 also have some similarities with Borysthenia goldfussiana , but they differ in smoother whorls and smoothed inflection of the whorls to the suture. In contrast, Borysthenia goldfussiana has less convex whorls and an angular inflection of the whorl to the suture (Gittenberger et al., 1998). Both Borysthenia pronaticina and Borysthenia goldfussiana are known from the Pliocene and Pleistocene deposits. The former species appeared in the Early Pliocene and is known from the Krutogorsky complex of the Western Siberia (Zykin, 2012). Borysthenia goldfussiana appeared in Northern Europe only in the Early Pleistocene (Tegelen) (Gittenberger et al., 1998). Regarding the late Maeotian age of our samples and their morphological similarity with Borysthenia pronaticina we treat them as Borysthenia cf. pronaticina (Lindholm, 1932) .

Region of distribution and age. Late Miocene – Pleistocene. Western Siberia, the Southern Urals, the south of Eastern Europe (Sanko, 2007; Zykin, 2012).

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.