Mohrensternia soceni Jekelius, 1944

Kowalke, Thorsten & Harzhauser, Mathias, 2004, Early ontogeny and palaeoecology of the Mid-Miocene rissoid gastropods of the Central Paratethys, Acta Palaeontologica Polonica 49 (1), pp. 111-134 : 130

Mohrensternia soceni Jekelius, 1944

Fig. 11B .

Mohrensternia soceni sp. nov.; Jekelius 1944: 71; pl. 15: 4–6. Mohrensternia soceni Jekelius ; Svagrovský 1971: 315–317, pl. 53:

1–5.

Material.— Four specimens from Siebenhirten, Vienna Basin , NHMW 2002 z0029/0013; two specimens from Hollabrunn, Molasse Basin , NHMW 2002 z0029/0012 (all Early Sarmatian).

Description.—The not very slender shell measuring up to 6 mm in height and up to 3 mm in width comprises up to seven regularly increasing whorls. Sculpture consists of 10 prominent axial ribs with about equally broad gaps between them. The axial ribs reach a maximum convexity on the lower half of the whorls, near the abapical suture, causing an angulated outline of the whorls. Spiral sculpture is absent. The last whorl forms 50–60% of total shell height. The aperture, which is slightly detached from the spire, has a rounded oval shape. It is characterised by a very thin peristome.

The protoconch comprises 2.5 rounded whorls measuring 0.45 mm in height and in maximum diameter. The embryonic shell amounts to 0.9 whorls measuring 0.15–0.16 mm in maximum diameter and 0.03–0.04 mm in the width of the initial cap. It is demarcated from the subsequent larval shell by a slightly thickened rim followed by a slight incision of the shell. The larval shell appears to be smooth. It is terminated by an indistinct rim. The onset of the teleoconch is indicated by the formation of axial folds, causing a wavy outline of the shell.

Remarks.—This species was originally described by Jekelius (1944) from the Early Sarmatian of Romania (Banat) . According to Svagrovský (1971) it also occurred in the Sarmatian of Slovakia.

Figures

Fig. 11. Four species of Mohrensternia Stoliczka, 1868. A. Mohrensternia pseudoangulata politioanei Jekelius, 1944. Specimen (NHMW 2002z0029/ 0009) from the Early Sarmatian of Waldhof, Styria/Austria (A1). Protoconch of the same specimen in lateral view (A2). The onset of the teleoconch is indicated by the formation of weak axial folds, grading into axial ribs. B. Mohrensternia soceni Jekelius, 1944. Specimen (NHMW 2002z0029/0012) from the Early Sarmatian of Hollabrunn (B1). Protoconch of the same specimen as in B1 in lateral view (B2). The onset of the teleoconch is indicated by the formation of axial folds. Detailed apical view of the initial whorl of the same protoconch as in B2 (B3). The embryonic shell is demarcated from the subsequent larval shell by a slightly thickened rim followed by an incision of the shell. C. Mohrensternia pfaffstaettensis sp. nov. Holotype (NHMW 2002z0029/0014) from the Early Sarmatian of Pfaffstätten, Vienna Basin/Lower Austria (C1). Lateral and apical view of the protoconch of the same specimen as in C1 (C2, C3). The protoconch is terminated by a slightly sinuous rim. The onset of the teleoconch is indicated by the formation of strong axial ribs and subordinated spiral threads. Detailed view of the initial whorl of the same protoconch as in C3 (C4). The embryonic shell has a finely granulated spiral sculpture. It is terminated by a slightly sinuous rim. D. Mohrensternia waldhofensis sp. nov. Holotype (NHMW 2002z0029/0004) from the Early Sarmatian of Waldhof, Styria/Austria (D1). Lateral and apical view of the protoconch of the same specimen (D2, D3). The transition to the teleoconch is indicated by a thickened rim which is not projecting.