Manzonia (M.) scalaris ( Dubois, 1831 )

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

Manzonia (M.) scalaris ( Dubois, 1831)

Fig. 8D .

Cyclostoma scalare Dubois de Montpereux 1831: 47 , pl. 3: 40, 41. Rissoa scalaris Dubois ; Hörnes 1856: 567, pl. 48: 12. Rissoa (Manzonia) scalaris Dubois ; Strausz 1966: 77: 42. Alvania (Taramellia) scalaris (Dubois) ; Bałuk 1975: 75, pl. 8: 13, 14.

Material.— Seven specimens from the Badenian of Steinebrunn , NHMW 2002 z0030/0019.

Description.—Dimensions of the teleoconch correspond to M. costata . Twelve axial ribs are present, crossed by 8 weaker spirals. The protoconch comprises 2.25 slightly rounded whorls measuring 0.38–0.39 mm in height and 0.36 mm in maximum diameter. The embryonic shell comprises one whorl measuring 0.06 mm in the width of the initial cap and 0.17–0.18 mm in maximum diameter. Sculpture consists of 6 spiral threads connected by short axial ribs. The transition to the larval shell is indicated by a thickened rim. The subsequent larval shell is sculptured by 2 weak spirals on the abapical half of the whorls. The protoconch is terminated by a well−developed sinusigera notch.

Remarks.—The protoconch indicates an indirect development including a free planktotrophic larval stage. M. scalaris differs from M. crassa by more but weaker−developed axial ribs, as well as by fewer and stronger−developed spirals. The protoconch differs by its larger size and by comprising about 0.25 whorls more. This widespread species is known from the Badenian of the Central Paratethys from Poland, Austria, Hungary, and Romania.

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.