Alvania (Alvania) schwartzi ( 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 : 122

Alvania (Alvania) schwartzi ( Hörnes, 1856)

Fig. 7D .

Rissoa Schwartzi Hörnes 1856: 573 , pl. 48: 18. Rissoa (Alvania) schwartzi Hörnes ; Strausz 1966: 75, pl. 46: 14–16. Alvania (? Galeodinopsis ) schwartzi (Hörnes) ; Bałuk 1975: 89, pl. 9: 3.

Material.— Ten specimens from the Badenian of Baden and five specimens from the Badenian of Steinebrunn , Lower Austria, NHMW 2002 z0030/0015.

Description.—The small stout shell comprises 5 flat to slightly rounded whorls measuring up to 2.1 mm in height and up to 1.4 mm in width. Sculpture consists of 16 straight axial ribs which are incised by 5–6 spiral grooves. The last whorl forms about 70% of total shell height. The base is sculptured by indistinct spiral threads. The large aperture has a drop shape, with a broad basal notch and a pointed parietal edge. It is characterised by a thickened outer lip which may bear indistinct teeth in its interior portion, and by a thin bent parietal and columellar lip.

The protoconch comprises 2.75 slightly rounded whorls measuring 0.45 mm in height and 0.42–0.43 mm in maximum diameter. The embryonic shell comprises one whorl, which measures 0.04 mm in the width of the initial cap and 0.16 mm in maximum diameter and which is well demarcated from the subsequent larval shell by a thickened rim on the shell. Embryonic ornament consists of dense, wavy spiral folds. The larval shell is sculptured by 6 prominent, zigzag−shaped spiral threads which are connected by very short axial threads. The protoconch is terminated by a well−developed sinusigera notch.

Remarks.—The protoconch is indicative of an indirect development including a free planktotrophic larval stage. The species is documented from the Badenian of Austria, Romania, Hungary, and Poland ( Meznerics 1933; Bałuk 1975). In Austria, Alvania (Alvania) schwartzi typically occurred in pelitic, offshore facies but is hardly recorded from sandy, littoral deposits, pointing to a preference for deeper−water environments.

Figures

Fig. 7. Four species of Alvania (Alvania) Risso, 1826. A. Alvania (Alvania) oceani (d’Orbigny, 1852). Specimen (NHMW 2002z0030/0012) from the Badenian of Steinebrunn, Lower Austria (A1). Protoconch of the same specimen as in A1 in lateral view (A2). The protoconch is terminated by a slightly thickened, fractionated sinusigera notch. B. Alvania (Alvania) perregularis (Sacco, 1895). Specimen (NHMW 2002z0030/0013) from the Early Badenian of Sedlec/Nový Rybník, Czech Republic (B2). Lateral and apical view of the protoconch of the same specimen as in B2 (B1, B3). The protoconch is terminated by a sinusigera notch. Detailed apical view of the initial whorl of the same protoconch as in B3 (B4). The embryonic shell consists of one inflated whorl, which is terminated by a thickened rim, reflecting the thickened apertural margin of the hatchling. C. Alvania (Alvania) transiens (Sacco, 1895). Specimen (NHMW 2002z0030/0014) from the Badenian of Steinebrunn, Lower Austria (C1). Protoconch of the same specimen as in C1 in lateral and apical view (C2, C3). The larval shell is sculptured by spiral rows of tubercles.It is terminated by a well developed sinusigera notch. D. Alvania (Alvania) schwartzi (Hörnes, 1865). Specimen (NHMW 2002z0030/0015) from the Badenian of Steinebrunn, Lower Austria (D2). Lateral and apical views of the protoconch of the same specimen as in D2 (D1, D3, D4). The protoconch is terminated by a well developed sinusigera notch. Detailed view of the initial whorl of the same protoconch as in D4 (D5). The embryonic shell is demarcated from the subsequent larval shell by a thickened rim.