Mohrensternia styriaca Hilber, 1897

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 styriaca Hilber, 1897

Mohrensternia Styriaca sp. nov.; Hilber 1897: 202, pl. 1: 11.

Mohrensternia styriaca Hilber ; Papp 1954: 36, pl. 5: 24–26, 28, 29.

Rissoa (Mohrensternia) angulata styriaca Hilber ; Boda 1959: 707, pl. 24: 17–21.

Mohrensternia styriaca Hilber ; Svagrovský 1971: 303–306, pl. 50: 1–7.

Material.— Three specimens from the Early Sarmatian of Siebenhirten , Lower Austria, IRSNB IG 23693 .

Description.—The slender, quite large shell is characterised by rounded whorls separated by deep sutures. It measures up to 6.2 mm in height and up to 3 mm in width. Sculpture consists of 10–12 strong axial ribs with broad and deep gaps. The ribs are strongly angulate in the mid portion, causing the angulate shell outline. Axial elements are crossed by distinct spiral threads. The last whorl amounts to about 50% of total shell height. The holostomatous aperture is roundish to oval with slightly pointed anterior and posterior portion.

The protoconch is not well preserved. It comprises about 2.25 well−rounded whorls measuring 0.35–0.36 mm in height and maximum diameter. The diameter of the first whorl is 0.16–0.17 mm. The onset of the teleoconch is indicated by the formation of axial folds, causing a wavy outline of the whorl.

Remarks.—Differs from the similarly slender morphs of M. pseudoangulata politioanei (which has strongly developed axial ribs) due to the larger last whorl and to its angular shell outline. The protoconch of M. styriaca differs by having a considerably larger initial whorl. The shell is similar to M. angulata , but is sculptured with axial ribs becoming larger in the mid portion of the whorls, causing a strongly angulated outline of the whorls.

According to Papp (1954), M. styriaca is common in the Early Sarmatian of Hollabrunn (Molasse Basin), Pfaffstätten (Vienna Basin), and Waldhof/Styria (Styrian Basin). According to Svagrovský (1971) and Iljina (1998) it co−occurred in the Sarmatian of the Pannonian Basin and of Slovakia.