Mohrensternia inflata ( Hörnes, 1856 )

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 : 127-128

Mohrensternia inflata ( Hörnes, 1856)

Fig. 10A, B .

Rissoa inflata ; Andrzejowsky in Deshayes 1835: 321, nomen nudum.

Rissoa inflata Andrzejowsky ; Hörnes 1856: 576, pl. 48: 22b.

Mohrensternia inflata (Andrzejowsky) ; Jekelius 1944: 69, pl. 14: 14–18.

Mohrensternia inflata (Andrzejowsky) ; Papp 1954: 34, pl. 5: 12–17.

Mohrensternia inflata (Andrzejowsky) ; Korobkov 1955: 155, pl. 21: 8a, b.

Rissoa (Mohrensternia) inflata inflata Andrzejowsky ; Boda 1959: 705, pl. 23: 6–11.

Mohrensternia inflata (M. Hoernes); Svagrovský 1971: 282–285, pl. 43: 1–12.

Mohrensternia inflata (Andrzejowsky) ; Ponder 1985: 77 G.

Material.— Five specimens from Hollabrunn, Lower Austria ( Molasse Basin ), NHMW 2002 z0029/0005; four specimens from Vienna−Nussdorf, Austria (Vienna Basin ), NHMW 2002 z0029/0006; six specimens from Vienna−Ottakring, Austria (Vienna Basin ), NHMW 2002 z0029/0007.

Description.—The comparatively large, thin shell has a broad, conical shape. It measures up to 8 mm in height and up to 5 mm in width, comprising 5–6 rounded, regularly increasing whorls with maximum convexity in the abapical half of the whorls. These are separated by distinct, moderately incised sutures. Twelve rounded orthocline to slightly opisthocyrt axial ribs are present, regularly following the outline of the whorls, with more or less broad gaps between them. Additional sculpture consists of regular, closely spaced, sinuous growth lines. Spiral sculpture is not evident. The last whorl forms about 60% of total shell height. The large holostomatous aperture is broad−oval and is characterised by a very thin peristome. The parietal portion is slightly pointed.

The large, conical, smooth protoconch comprises 2.5 rounded whorls measuring 0.43–0.44 mm in height and 0.4–0.42 mm in maximum diameter. The embryonic shell comprises 0.8–0.9 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 separated from the subsequent larval shell by a slightly thickened rim on the shell. The transition from the larval shell to the teleoconch is indistinct. The onset of the adult shell is indicated by the formation of weak, indistinct axial folds that grade into regular axial ribs.

Remarks.—Specimens with slightly sickle−shaped axial ribs have been described by Friedberg (1923) and have been assigned to Mohrensternia perinflata Friedberg , which most probably represents a synonym of M. inflata ( Svagrovský, 1971) . Our material from the Vienna Basin exhibits several specimens with opisthocyrt course of the axial ribs, but with identical protoconch and teleoconch dimensions fully corresponding to specimens with orthocline ribs.

Mohrensternia inflata differs from M. angulata ,which has a similar sculpture, by its considerably larger protoconch and by a broader teleoconch. It is distinguished from M. hollabrunnensis sp. nov. with similar outline by its considerably larger protoconch, which is higher than wide (versus wider than high in M. hollabrunnensis ). The latter differs furthermore by its teleoconch sculpture of more and weaker axial ribs.

Papp (1954) also described Mohrensternia inflata from Early Sarmatian deposits of Heiligenstadt, Pfaffstätten, and Siebenhirten (Vienna Basin, Austria). According to Svagrovský (1971) this species is widespread in Early Sarmatian deposits of the Mid Danube Basin and of the Carpathian Foredeep. Iljina (1998) mentioned its occurrence in Early Sarmatian deposits of SE Europe and in Middle Sarmatian deposits of Georgia.

Figures

Fig. 10. Two species of Mohrensternia Stoliczka, 1868. A, B. Mohrensternia inflata (Hörnes, 1856). A. Specimen (NHMW 2002z0029/0005) from the Early Sarmatian of Hollabrunn. B. Specimen (NHMW 2002z0029/0006) from the Early Sarmatian of Vienna−Nussdorf. Protoconch in lateral (B2) and apical (B3) views. The embryonic shell is separated from the subsequent larval shell by a slightly thickened rim. The onset of the teleoconch is indicated by the formation of weak axial folds, grading into regular axial ribs. C. Mohrensterniamoesinensis Jekelius, 1944. Specimen (collection A. Papp, NHMW 2002z0029/ 0008) from the Early Sarmatian of Eichkogel (C1). Lateral views of the protoconch of the same specimen as in C1 (C2, C3). The protoconch is terminated by a slightly projecting rim, which is slightly thickened in its adapical portion. Detailed apical view of the initial whorl of the same protoconch as in C3 (C4). The embryonic shell has fine spiral sculpture and it is terminated by a slightly thickened rim.