Tectura zboroviensis Friedberg, 1928

Anistratenko, Olga Yu., Bandel, Klaus & Anistratenko, Vitaliy V., 2006, A new genus of patellogastropod with unusual protoconch from Miocene of Paratethys, Acta Palaeontologica Polonica 51 (1), pp. 155-164 : 161-162

Tectura zboroviensis Friedberg, 1928

Fig. 5C .

1928 Tectura zboroviensis sp. nov.; Friedberg 1928: 536, pl. 35: 8a, 8b.

Type material: Three specimens from the late Badenian of Zborów , Ukraine ( Friedberg 1911 –1928) . The material is stored in the Geological Museum of the Institute of Geological Sciences PAS (Kraków, Poland) .

Material.— Sixteen specimens from the Chokrakian of Yurkino locality ( IGS NANU 18 /2003–34/2003) ; seventeen specimens from the late Badenian of Varovtsy locality ( IGS NANU 1 /1980–17/1980) ; nine specimens apparently of this species have been found in early Sarmatian deposits of Veselyanka locality ( IGS NANU 1 /2003–17/2003), Ukraine .

Description.—Specimens of Tectura zboroviensis from the late Badenian of western Ukraine (Varovtsy) have a limpet−like moderately high shell. The apex in adult specimens is positioned almost centrally, but in juvenile individuals it is somewhat tilted backward, the apical angle (measured from the front view) varies about 70–80 ° in different specimens. Sculpture consists of numerous (up to 20) but rather fine radial ribs crossed by the growth lines. The outer sculptured layer is often peeled off and the surface of teleoconch in most adult individuals appears smooth. The aperture is broad oval ( Fig. 5C 1 –C 3 ).

The studied specimens of Tectura zboroviensis from the Chokrakian of the Kerch region and early Sarmatian of the southern Ukraine (Veselyanka) are characterized by elongated, cup−shaped, ventrolaterally inflated protoconchs. They measure from 0.08 mm to 0.10 mm in length and about 0.10 mm in width, and are situated in an asymmetrical position relative to the sagittal axis of the teleoconch. The surface of the protoconch is smooth ( Fig. 5C 4). The transition from the embryonic shell to the early teleoconch is usually quite distinct, defined by a small constriction or by a rim of the aperture of the protoconch shell. This feature may have formed when the veliger was ready to settle for benthic life and begin construction of the teleoconch with adult sculpture. The later, relatively extended part of the juvenile teleoconch reaches up to 0.2 mm in width and is covered by fine lines parallel to the axis of the protoconch.

The protoconch shape, dimensions and proportions indicate indirect development including a free swimming, but non−feeding, veliger larva.

Dimensions.— The studied shells measure up to 2.8 mm in length, 1.8 mm in width and 1.3 mm in height. Friedberg (1928) has presented similar data for Tectura zboroviensis from the type locality ( Zborov town , Lviv region, Ukraine): up to 2.6 mm in length, 2.0 mm in width and 1.5 mm in height .

Discussion.—Modern representatives of Tectura (sometimes included in Acmaea ) from the Mediterranean Sea and from the North Atlantic are characterized by a protoconch morphology similar to Tectura zboroviensis . One specimen of Tectura virginea ( Müller, 1776) from the Mediterranean Sea has been documented but not published yet by Anders Warén (Swedish Museum of Natural History, Stockholm) who kindly provided SEM photo of that specimen. This Recent form has nearly the same protoconch dimensions as Tectura zboroviensis , but it is distinguished by a more bulbous embryonic shell.

Stratigraphic and geographic range.— Tectura zboroviensis was originally described from the late Badenian of the Central Paratethys (Friedberg 1928). It was encountered recently in our material from Chokrakian of the Eastern Paratethys (coeval with middle Badenian of the Central Paratethys).

Bałuk (1975: 20–30, figs. 9, 10) documented Acmaea (Tectura) friedbergi Bałuk, 1975 from the Lower Badenian of Poland, and Strausz (1966) found Acmaea sp. from Hungary. But these authors noted that a more detailed comparison between these and others described forms or species is not possible. Judging from the similar shell shape and also their occurrence in beds of the same or similar stratigraphical age (that is Badenian) it is quite possible that Acmaea friedbergi represents a species with the same type of protoconch as Tectura zboroviensis .

Figures

Fig. 5. Blinia gen. nov. and Tectura Gray, 1847 from Miocene of Ukraine. A. Blinia angulata (d’Orbigny, 1844). Specimen (IGS NANU 1/2004) from the middle Sarmatian of Letichev, apical view (A1). Lateral view of the same specimen (A2). B. Blinia pseudolaevigata (Sinzov, 1892). Specimen (IGS NANU 41/2004) from the middle Sarmatian of Letichev, apical view (B1). Lateral view of the same specimen (B2). Detailed apical view of the embryonic shell and juvenile teleoconch of the same specimen as in B1 (B3). The embryonic shell is ornamented by fine concentric wrinkles and pit on the apex. C. Tectura zboroviensis (Friedberg, 1928). Specimen (IGS NANU 18/2003) from the Chokrakian of Yurkino, apical view (C1). Lateral and frontal views of the same specimen (C2, C3). Detailed apical view of the embryonic shell and juvenile teleoconch of the same specimen as in C1 (C4). The onset of juvenile teleoconch is ornamented by fine spiral threads. D. Blinia sp. Specimen (IGS NANU 4/2004) from the middle Sarmatian of Letichev. Detailed apical view of the embryonic shell and juvenile teleoconch.

Fig. 3. A sketch drawing of the inner shell surface of Blinia sp. with muscle scars indicated by arrows. Specimen (IGS NANU 88/2004) from the middle Sarmatian of Letichev. Anterior edge of a shell is on the top.