Manzonia (Alvinia) partschi ( 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 : 124-125

Manzonia (Alvinia) partschi ( Hörnes, 1856)

Fig. 8B .

Rissoa partschi sp. nov.; Hörnes 1856: 573–574, pl. 48: 19 a, b.

Manzonia partschi (Hörnes) ; Meznerics 1933: 332.

Rissoa (Manzonia) partschi (Hörnes) ; Strausz 1966: 77, pl. 46: 23.

Alvania (Manzonia) partschi (Hörnes) ; Bohn−Havas 1973: 1038, pl. 3: 8.

Alvania (Taramellia) partschi (Hoernes) ; Gürs and Weinbrecht 2001: 82, fig. 2.10, pl. 1: 11.

Material.— Fourteen specimens from the Badenian of Baden / Sooss , Lower Austria, NHMW 2002 z0030/0017.

Description.—The slender, conical shell comprises 6 rounded whorls measuring up to 5 mm in height. The last whorl forms about 60% of total shell height. Sculpture consists of 20 weak, straight to slightly opisthocyrt axial ribs, which are crossed by 4 about equally strong spiral keels forming a very regular reticulate pattern. The points of intersection of axial and spiral sculptural elements are thickened. Nodes to very short spines are formed. The base is sculptured by two prominent spiral keels. The large, rounded, egg−shaped, holostomatous aperture is characterised by a circular pad.

The protoconch has 2.5 slightly rounded whorls measuring 0.41–0.43 mm in height and 0.39–0.43 mm in maximum diameter. The embryonic shell comprises nearly one inflated whorl measuring 0.06–0.07 mm in the width of the initial cap and 0.15–0.16 mm in maximum diameter. It is strongly sculptured by 7 spiral threads connected by weak short axial threads. The embryonic shell is terminated by a slightly sinuous rim. The subsequent larval shell is sculptured by 8 spiral threads which may be disconnected, building rows of elongated nodes. The rows are strongest developed in the median portion of the whorls. The protoconch is terminated by a short, slightly thickened sinusigera notch.

Remarks.—The protoconch points to indirect development including a free planktotrophic larval stage. Manzonia (Alvinia) partschi differs from M. (A.) miocrassicosta by its larger, slen− der, less thickened shell and by its weaker−developed sculpture of more but delicate axial ribs. The protoconch differs by its considerably larger size and stronger−developed embryonic and larval sculpture. M. (A.) partschi is very similar to the type species but differs by its slightly weaker sculpture and by its indirect mode of early ontogenetic development. M. (A.) partschi is a rather rare species which is known in the Central Paratethys from Hungary, Austria, and Romania. Janssen (1984) and Gürs and Weinbrecht (2001) described this species from the Miocene of the North Sea Basin.

Figures

Fig. 8. Two species of Manzonia (Alvinia) Monterosato, 1884 and two of Manzonia (Manzonia) Brusina, 1870. A. Manzonia (Alvinia) miocrassicosta (Sacco, 1895). Specimen (NHMW 2002z0030/0016) from the Badenian of Steinebrunn (A1). Lateral and apical view of the protoconch of the same specimen (A2, A3). The protoconch is terminated by a short sinusigera notch. Detailed view of the initial whorl of the same protoconch as in A3 (A4). The embryonic shell is demarcated from the subsequent larval shell by a well developed thickened rim. B. Manzonia (Alvinia) partschi (Hörnes, 1856). Specimen (NHMW 2002z0030/0017) from the Badenian of Baden/Sooss, Lower Austria (B1). Lateral and apical view of the protoconch of the same specimen as in B1 (B2, B3). The protoconch is terminated by a short, slightly thickened sinusigera notch. Detailed view of the initial whorl of the same protoconch as in B3 (B4). The embryonic shell is strongly sculptured and terminated by a slightly sinuous rim. C. Manzonia (Manzonia) crassa (Kanmacher in J. Adams, 1798), specimen (NHMW 2002z0030/0018) from the Badenian of Niederleis, Lower Austria. D. Manzonia (Manzonia) scalaris (Dubois, 1831). Specimen (NHMW 2002z0030/0019) from the Badenian of Steinebrunn, Lower Austria (D1). Lateral and apical view of the protoconch of the same specimen as in D1 (D2, D3). The protoconch is terminated by a well developed sinusigera notch. Detailed view of the initial whorl of the same protoconch as in D3 (D4). The transition to the larval shell is indicated by a thickened rim.