Obsoletiformes obsoletum ingratum (Kolesnikov, 1929)

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 : 22

Obsoletiformes obsoletum ingratum (Kolesnikov, 1929)

Figure 3.7-8

1929 Cardium ingratum Kolesnikov , p. 13, pl. 4, figs. 95-101.

1935 Cardium ingratum Kolesnikov ; Kolesnikov, p. 93, pl. 11, figs. 10-16.

1969 Cardium (Cerastoderma) ingratum (Kolesnikov) ; Kojumdgieva, p. 30, pl. 9, figs. 7, 8.

1993 Obsoletiforma obsoleta ingrata (Kolesnikov) ; Nevesskaya, Goncharova, Paramonova, Popov, Babak, Bagdasaryan, and Voronina, p. 248, pl. 57, figs. 15-18.

2001 Obsoletiformes obsoletus ingratum (Kolesnikov) ; Nevesskaja, Paramonova, and Popov, p. 180.

Material. 11 specimens from layer 1 (10 left valves, 11 right valves).

Description. Round-triangular shell (LS up to 15.5 mm; HS up to 14.5 mm; Con. up to 5 mm), equivalve. Closure of the valves is dense. Umbo is pointed, curved, and slightly shifted forward. The anterior branch of the dorsal edge is gently sloped and without noticeable angles merges into a widely rounded anterior edge. The posterior branch of the dorsal edge forms a well-defined blunt angle with a slightly convex (almost straight) posterior edge. Ventral edge slightly convex. Valves slightly inequilateral, convex. The keel bend is rounded. The shell surface is covered with rectangular ribs. The number of ribs in our material is up to 24. The intercostal distance is slightly narrower than the ribs. The ribs are smooth. Growth lines and growth stop lines are clearly visible on the shell surface.

There are two cardinal teeth, two anterior lateral teeth (the lower one is more developed), and one posterior lateral tooth in the right valve. In the left valve one cardinal tooth and two lateral teeth, posterior are weakly developed. There is a nymph behind the umbo. Nymph is about 1/3 of the posterior branch of the dorsal edge. The pallial line is whole. The scars of the anterior and posterior muscles are round-oval, approximately equal in size. There are grooves corresponding to the ribs on the inner surface. On the edge of the shell they take the form of “serration”.

Remarks. Species epithet has been changed from obsoletus to obsoletum (Nevesskaya et al., 2013) .

Region of distribution and age. Middle Sarmatian (Bessarabian) of the Eastern Paratethys (Nevesskaya et al., 1993).

Figures

FIGURE 3. Assemblage of the Middle Sarmatian (Bessarabian) marine bivalves (layer 1). 1-2, Polititapes ponderosa (d’Orbigny, 1844). 3-4, Polititapes vitaliana (d’Orbigny, 1844). 5-6, Sarmatimactra fabreana (d’Оrbigny, 1844). 7-8, Obsoletiformes obsoletum ingratum (Kolesnikov, 1929). 9-10, Obsoletiformes obsoletum obsoletum (Eichwald, 1830). 11, Plicatiforma fittoni fittoni (d’Orbigny in Murchison et al., 1845). 12-13, Ervilia dissita dissita (Eichwald, 1830).

FIGURE 4. Assemblage of the Middle Sarmatian (Bessarabian) marine gastropods (layers 1 and 2). 1, Acteocina lajonkaireana (Basterot, 1825). 2, Acteocina okeni (Eichwald, 1850). 3, Retusa melitopolitana (Sokolov, 1899). 4, Hydrobia elongata Eichwald, 1830. 5, Pseudamnicola nympha (Eichwald, 1850). 6, Dorsanum duplicata opinabile (Kolesnikov, 1932). 7, Dorsanum corbiana (d’Orbigny, 1844). 8, Dorsanum ignobile (Kolesnikov, 1932). 9, Gibbula (Gibbula) pseudoangulata (Sinzov, 1875). 10, Gibbula (Sarmatigibbula) podolica (Du Bois de Montpéreux, 1831).

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.

FIGURE 6. Assemblage of the Maeotian terrestrial molluscs (layer 3). 1, cf. Helicella sp. 2, Helicodiscus (Helicodis- cus) roemeri (Andreae, 1902). 3, Vallonia cf. pulchella (Müller, 1774). 4-5,? Deroceras sp.

FIGURE 7. Assemblage of the redeposited Miocene marine and terrestrial molluscs. 1, Vertigo sp. 2, Hydrobia enikalensis Kolesnikov, 1935. 3, Hydrobia elongata Eichwald, 1830. 4, Gibbula sp. 5, Gibbula (Sarmatigibbula) podolica (Du Bois de Montpéreux, 1831). 6, Gibbula sp. 7, Acteocina lajonkaireana (Basterot, 1825).

FIGURE 8. Assemblage of the redeposited Miocene marine and terrestrial molluscs. 1, Dorsanum sp. 2, Gibbula (Gibbula) pseudoangulata (Sinzov, 1875). 3, Anisus cf. spirorbis (Linnaeus, 1758). 4, Blinia cf. angulata (d’Orbigny, 1844). 5, Cardiidae indet. (cf. Obsoletiformes). 6, Cardiidae indet. 7, Barbotella intermedia (Radovanović et Pavlović, 1893).