Mohrensternia waldhofensis, Kowalke & Harzhauser, 2004

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 : 131

Mohrensternia waldhofensis sp. nov.

Fig. 11D .

Derivation of the name: Named after the type locality.

Type horizon and locality: Early Sarmatian , silty to marly brackish water clay at Waldhof near Wetzelsdorf, Styria / Austria .

Material.— The holotype ( NHMW 2002 z0029/0016) and two paratypes ( NHMW 2002 z0029/0017) are present from the Early Sarmatian of Waldhof , Styria .

Description.—The small, moderately slender, turreted shell comprises up to seven slightly rounded whorls separated by moderately incised sutures. The holotype measures 3.42 mm in height and 1.64 mm in width. Sculpture consists of 12 regularly rounded, broad axial ribs, about as broad as the gaps between them. Indistinct, subordinated spiral striae cross the axial ribs. The last whorl forms about 50% of total shell height. The oval aperture is thin, holostomatous and is characterised by a slightly pointed posterior portion. A very narrow, slit−like umbilicus is present.

The broad, barrel−shaped protoconch comprises 2.25 slightly rounded whorls measuring 0.34 mm in height and 0.29 mm in maximum diameter. The first whorl measures 0.12–0.13 mm in maximum diameter and 0.04 mm in the width of the initial cap. The transition from the embryonic shell to the larval shell is indistinct. The transition from the larval shell to the teleoconch is indicated by a straight, thickened rim, which is not projecting.

Remarks and differences.—The protoconch indicates an indirect development including a free planktonic larval stage. Mohrensternia waldhofensis sp. nov. differs from M. banatica (which has a similar size and outline) by the higher body whorl and the coarser sculpture of fewer but stronger axial ribs. The protoconch of M.waldhofensis is higher than wide, whereas it is as high as wide in M. banatica , which is furthermore distinguished by a well−demarcated embryonic shell. Mohrensternia waldhofensis differs from M. angulata (with similar sculpture) by its smaller shell and by the oval aperture, which is more rounded in M. angulata . The protoconch differs in being higher than wide in M.waldhofensis (as high as wide in M.angulata ).

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.