Mohrensternia pseudoangulata politioanei Jekelius,

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 : 129

Mohrensternia pseudoangulata politioanei Jekelius,

1944

Fig. 11A .

Mohrensternia pseudoangulata politioanei n. var.; Jekelius 1944: 72, pl. 15: 11–15.

Mohrensterniapseudoangulatapolitioanei Jekelius; Svagrovský 1960: 76, pl. 5: 5.

Mohrensterniapseudoangulatapolitioanei Jekelius; Svagrovský 1971: 299–301, pl. 48: 1–7.

Material.— Four specimens from the Early Sarmatian of Waldhof, Styrian Basin , NHMW 2002 z0029/0009; two specimens from Siebenhirten, Vienna Basin , NHMW 2002 z0029/ 0010; 3 specimens from Hollabrunn, Molasse Basin , NHMW 2002 z0029/0011 (all Early Sarmatian).

Description.—The slender shell comprises 6–7 regularly increasing whorls measuring up to 7 mm in height and up to 2.8 mm in width. The rounded whorls are separated by deep sutures. Sculpture consists of 10–12 strongly developed orthocline axial ribs with broad gaps between them, crossed by 12 fine spiral threads. The last whorl forms 50% of total shell height. The holostomatous aperture has an inclined, oval shape. It is characterised by a thin peristome and by a pointed anterior and posterior portion.

The protoconch comprises 2.25–2.3 rounded whorls measuring 0.34–0.35 mm in height and 0.35–0.36 mm in maximum diameter. The embryonic shell comprises 0.8–0.9 whorls measuring 0.12–0.13 mm in maximum diameter and 0.04–0.05 mm in the width of the initial cap. The transition to the larval shell is indicated by a slight rim on the shell. The larval shell appears to be smooth. The transition to the teleoconch is indistinct. The onset of the adult shell is indicated by the formation of weak axial folds that grade into strong axial ribs.

Remarks.—The protoconch is indicative of an indirect development including a free planktonic veliger stage. M. pseudoangulata politioanei differs from M. pseudoangulata pseudoangulata Hilber, 1897 by its considerably less slender shell. It furthermore differs by its less angular outline. It differs from M. banatica by its slightly smaller protoconch but slightly larger cap−like onset of the embryonic shell, and by its less slender shell with less strongly developed axial ribs, which not orthocline in course. Mohrensternia pseudoangulata politioanei is distinguished from the similar M. angulata by its slightly smaller embryonic shell, but slightly larger initial cap, and by the lack of spiral sculpture on the teleoconch whorls.

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.