Gyraulus cf. acronicus (Férrussac, 1807)

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 : 16

Gyraulus cf. acronicus (Férrussac, 1807)

Figure 5.8

1807 Planorbis acronicus Férussac , p. 105.

1964 Gyraulus acronicus (Férussac) ; Ložek, p.

188.

1998 Gyraulus (Gyraulus) acronicus (Férussac) ; Gittenberger, Janssen, Kuijper, Kuiper, Meijer, Velde and Vries, p. 151, figs. 321- 323, 363.

2002 Gyraulus (Gyraulus) acronicus (Férussac) ; Glöer, p. 270, add. 291.

2007 Gyraulus acronicus (Férussac) ; Sanko, p.

127, fig. 96.

Material. 94 specimens from layer 3.

Description. Planispiral shell (HS is 1.1-1.5 mm, average 1.26; WS is 3.6-4.0 mm, average 3.6; WS/ HS is 2.6-4, average 3.6) consists of 4-4.5 rounded whorls separated by a deep suture, increasing fast and evenly in width. Protoconch consists of 1.5 whorls. The last whorl is about twice as wide as the penultimate one. On the periphery of the last whorl there is an inflection (keel), which is located in the middle or displaced downwards. On the upper side, the whorls are sloping; the lower side is more rounded. Aperture is oval, oblique, slightly lowered, without a lip (HA is 1.1-1.6, average 1.3; WA is 1.3- 2.4, average 1.7). The shell surface is transversely striated; weak spiral lines are present.

Region of distribution and age. Pliocene – Present. Asia, Europe, America (Glöer, 2002). 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.