Alvania (Alvania) transiens (Sacco, 1895)

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 : 121-122

Alvania (Alvania) transiens (Sacco, 1895)

Fig. 7C .

Rissoa venus d’Orbigny ; Hörnes 1865: 565–566, pl. 48: 10 a, b.

Alvania sculpta ? var. transiens Sacco 1895: 27 .

Alvania venus d’Orbigny var. danubiensis Cossmann and Peyrot ; Meznerics 1933: 331.

Alvania (Alvania) venus (d’Orbigny) ; Steininger 1963: 43, pl. 13: 1.

Rissoa venus danubiens Cossmann and Peyrot ; Strausz 1966: 72–73, pl. 48: 17, 18.

Alvania venus danubiensis Cossmann and Peyrot ; Bohn−Havas 1973: 1037.

Alvania (Acinulus) venustransiens Sacco ; Bałuk 1975: 86, pl. 9: 18, 19.

Material.— Eight specimens from the Badenian of Steinebrunn , Lower Austria, NHMW 2002 z0030/0014.

Description.—The elongate, egg−shaped shell comprises 6 flat to slightly rounded whorls separated by deep sutures. The shell measures up to 3 mm in height. The teleoconch sculpture consists of 16 straight axial ribs crossed by 6 about equally strong spiral cords forming a very regular reticulate pattern. Nodes are developed in the points of intersection of the axial and spiral sculptural elements. The last whorl forms about 70% of total shell height. It is elongate cylindrical, whereas the spire is conical. The aperture has a drop shape with pointed parietal portion. A faint, broad anterior notch is present. The columellar lip is bent. The interior portions of the outer and basal lip are characterised by more or less strongly developed teeth.

The conical protoconch comprises 2.75 slightly rounded whorls measuring 0.48 mm in height and 0.43 mm in maximum diameter. The embryonic shell comprises one whorl measuring about 0.05 mm in the width of the initial cap and 0.13–0.14 mm in maximum diameter. Remains of fine spiral threads are present on the embryonic shell. It is terminated by a slightly thickened rim on the shell. The larval shell bears 10 spiral rows of coarse tubercles. It is terminated by a well−developed sinusigera notch.

Remarks.—The shells have usually been treated as Alvania venus ( d’Orbigny, 1852) or as a subspecies thereof. Indeed, the Paratethyan specimens differ considerably in their less convex whorls, the more angulated aperture and the characteristic, deep, angulated suture which separates the penultimate whorl strongly from the body whorl. Alvania venus from the Aquitanian of France, illustrated by Lozouet et al. (2001), clearly documents these differences and furthermore reveals a much coarser sculpture with rather pointed nodes. In contrast, the protoconchs of both discussed species are very similar (see protoconch of Alvania venus in Lozouet et al. 2001: pl. 13: 5b, c).

Cossmann and Peyrot (1919) correctly recognised the differences of the Paratethyan species from Alvania venus and consequently introduced the new name Alvania venus var. danubiensis . Twenty−four years earlier, however, the same conclusions already prompted Sacco (1895) to separate the Paratethyan shells as var. transiens .

Alvania (Alvania) transiens resembles Alvania (Alvania) perregularis , but differs by its coarser teleoconch sculpture and by an acute conical protoconch, which is higher than wide, whereas the protoconch of Alvania (A.) perregularis is about as wide as high. The embryonic shell of Alvania (A.) transiens is considerably smaller than that of A. (A.) perregularis . Alvania anabaptizata Boettger, 1901 , and the specimens described as Alvania sculpta ( Philippi, 1836) by Boettger (1901) from the Early Badenian of Romania are considered as synonyms of Alvania transiens by Bałuk (1975). Alvania transiens appears in the Central Paratethys during the Early Miocene (Eggenburgian) and is an ubiquitous Paratethyan species up to the Late Badenian.

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.