Lithoglyphus acutus Cobălcescu, 1883

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 : 14-15

Lithoglyphus acutus Cobălcescu, 1883

Figure 5.2-3

1883 Lithoglyphus acutus Cobălcescu , p. 145, pl. 14, fig. 10.

1896 Lithoglyphus acutus Cobălcescu ; Stefanescu, p. 112, pl. 10, figs. 58-63.

1919 Lithoglyphus sarmaticus Bogachev and Shishkina , p. 38-39.

1924 Lithoglyphus acutus Cobălcescu ; Bogachev, p. 215, pl. 7, figs. 53, 55, 56.

1929 Lithoglyphus acutus Cobălcescu ; Mangikian, p. 171, pl. 1, fig. 9.

1942 Lithoglyphus acutus acutus Cobălcescu ; Wenz, p. 48, pl. 15, figs. 195-198.

1962 Lithoglyphus carinatus Popov , p. 94 [nomen nudum].

1972 Lithoglyphus acutus Cobălcescu ; Popov, p. 101, pl. 9, figs. 23-26.

1972 Lithoglyphus acutus carinatus Popov , p.

101, pl. 9, figs. 20-23.

Material. 1410 specimens from layer 3 (among them 131 specimens with a noticeable keel inflection).

Description. Oval-conical shell with pointed spire

(HS is 6.6-8.2 mm, average 7.3; WS is 4.5-6.3 mm,

average 5.6), low (WS/HS is 0.7-0.8, average

0.74), consisting of 5 rounded whorls separated by a shallow suture. The last whorl is rounded, sometimes with slight inflection, almost 3/4 of the height of the shell (HLW/HS is 0.8-0.9, average 0.83). Aperture has an ovoid form, large, pointed at the upper part (WA/HA is 0.7-0.8, average 0.73), is about 1/2 of the total shell height (HA/HS is 0.6- 0.7; 0.61). The outer edge of the aperture is thin; the inner is thickened. Umbilicus is closed by the inner edge of the aperture or in the form of a narrow slit. Fine hatching covers the shell surface.

Remarks. The collection contains numerous Lithoglyphus among which a small group is distinguished due the presence of a keel. It is expressed in smooth bend of the last whorl towards slightly inclined area adjacent to the suture. Some roughness of the last whorl (“hammered surface”) on the outer lip side and on the side opposite to the aperture is observed as well.

Bogachev (1924) identified Lithoglyphus naticoides (Pfeiffer, 1828) and L. fluminensis Schmidt, 1847, in the deposits of the Morskaya 2 site. Popov (1972, p. 101-102) considered that the comparison with Lithoglyphus naticoides as incorrect, and argued that Lithoglyphus from the Morskaya 2 site differs from L. fluminensis in the higher and more pointed spire. Popov (1972) attributed the Lithoglyphus of the M orskaya 2 site to the species Lithoglyphus acutus Cobălcescu, 1883. Comparison of specimens from our collection with images of L. acutus given by different authors (Cobălcescu, 1883; Stefanescu, 1896; Bogachev, 1924; Mangikian, 1929; Wenz, 1942; Popov, 1962, 1972) confirmed this attribution.

Bogachev and Shishkina (1919) described a shell with a keel as a new species Lithoglyphus sarmaticus. The drawing of this species (Bogachev and Shishkina, 1919, p. 38) demonstrates clearly visible keel on the last whorl. Later this species was mentioned only by Kolesnikov (1934); Bogachev did not use this species name in his publications anymore.

Popov (1962) attributed Lithoglyphus with a keel also as a new species Lithoglyphus carinatus, but without descriptions or images (nomen nudum). Later Popov (1972, p. 101) described the Akchagylian Lithoglyphus of the Akkulaevo site in Fore-Urals and synonymised the species L. carinatus G. Popov under L. acutus Cobălcescu Popov (1972) noticed that both species are morphologically similar and that the keel is present occasionally. For these Lithoglyphus with keel he described new subspecies – Lithoglyphus acutus carinatus G. Popov (1972, 101, pl. 9, fig. 20-23). A slightly concave bend to the suture and a small shaft are also present on the specimens described by Cobălcescu for his L. acutus from the Dacian Basin (1883, p. 145, tabl. XIV, fig. 10), but absent on the photographs depicting this species given by S. Stefanescu (1896, p. 112, pl. 10, figs. 58-63) and Wenz (1942, p. 48, pl. 15, figs. 195-198). We support the opinion of Popov (1972) and assume that our Lithoglyphus with keel is phenotype of Lithoglyphus acutus, and species Lithoglyphus sarmaticus and Lithoglyphus acutus carinatus are junior synonyms.

Variability. Sometimes obviously pronounced inflection appears at the last rounded whorl, which is clearly visible near the aperture ( Figure 5.3 ).

Region of distribution and age. Late Miocene – Pliocene of the northern Black Sea region and Azov Sea region (Popov, 1972).

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.