Bittium acutum Ossaulenko, 1936

Bittium acutum Ossaulenko, 1936

Figs 2A–D View FIGURE 2

* Bittium acutum sp. nov. — Ossaulenko 1936: 86, pl. 3, figs 19–26.

Bittium acutum Ossaulenko, 1937 — Zelinskaya et al. 1968: 162.

Bittium acutum Osaulenko— Iljina et al. 1976: 99 , pl. 25, figs 20–22.

? Bittium sp. — Badzoshvili 1986: 63, pl. 19, fig. 1.

Type material. Lectotype designated herein: specimen illustrated in Ossaulenko (1936: pl. 3, fig. 21); not seen, size not given. Stored in the Geological Museum in Kiev ( Ukraine). Bila Krynytsya ( Ukraine), Late Miocene, early Maeotian.

Illustrated material. PIN 5904/2, SL: 4.4 mm, MD: 1.5 mm, Figs 2A View FIGURE 2 1 –A View FIGURE 1 2 View FIGURE 2 . PIN 5904/4, SL: 4.8 mm, MD: 1.8 mm, Figs 2B View FIGURE 2 1 –B View FIGURE 1 3 View FIGURE 3 . PIN 5904/5, SL: 4.3 mm, MD: 1.5 mm, Fig. 2C View FIGURE 2 . PIN 5904/6, SL: 4.3 mm, MD: 1.7 mm, Fig. 2D View FIGURE 2 . All specimens from Bila Krynytsya ( Ukraine), early Maeotian, Late Miocene.

Revised description. Small, slender shell of about 9–10 teleoconch whorls, attaining 5.5–7 mm in height; apical angle 20–25°. Protoconch unknown. Whorl profile angled with broad subsutural ramp, weakly convex below. Suture incised, linear. First two teleoconch whorls with two prominent primary spiral cords placed mid-whorl and third cord along abapical suture. First secondary spiral cord appears above upper primary cord on second whorl; abapically, second secondary cord follows above first secondary cord, and third secondary cord intercalated between two earlier secondary spiral cords. Last two whorls bear up to six or seven cords and threads. Two upper primary cords wider and more prominent, suprasutural cord only partially visible. Adapical primary cord widest, bearing largest nodes, if present, placed mid-whorl coinciding with maximum diameter and angulation. Spirally elongated beads usually prominent in middle part of teleoconch; weakening to subobsolete on last two whorls. Beads widely spaced, around 10–13 per whorl. Single poorly developed varix may be located close to aperture in fully adult shells. Microsculpture of close-set spiral rows of tiny tubercles in spiral interspaces and minute pits over cords. Last whorl strongly constricted, attaining 38–41% of total height. Base with two prominent peribasal spiral cords; and two further thinner cords over base in most specimens. Aperture wide, ovate. Columella excavated. Columellar callus forming thin, moderately broad rim.Anal canal indistinct, V-shaped. Outer lip thin. Siphonal canal very short, wide.

Discussion. The species is mostly known from the type area. It differs from Bittium badzoshviliae sp. nov. in the less prominent spiral sculpture with weakly angled to convex whorls. Bittium acutum Ossaulenko, 1936 is also more slender than Bittium badzoshviliae .

Iljina (1976: pl. 25, fig. 19) illustrated a poorly preserved, very slender shell devoid of axial sculpture from Cape Urdek ( Kazakhstan) as this species. A sample from that locality yields only poorly preserved and undeterminable shells. These may be morphs of B. acutum or slender morphs of Bittium bosphoranum ( Andrussow, 1890) with poorly developed axial sculpture. Badzoshvili (1976: pl. 19, fig. 1) also illustrated a shell which is very close to B. acutum , but that specimen lacks axial sculpture, which would be atypical for B. acutum . Moreover, the shell was found outside the known distribution area of that species.

Bittium acutum is transitional between B. bosphoranum and B. badzoshviliae . We assume that B. acutum derived from B. bosphoranum , becoming more slender and less sculptured. Subsequently, B. badzoshviliae derived from B. acutum developing more prominent axial ribs and primary cords, whilst its secondary sculpture became reduced. Especially near the Caucasian area, B. acutum develops shells that are reminiscent of B. badzoshviliae .

Paleoenvironment. Shallow marine, inner neritic, based on associated fauna (own data A.G.).

Distribution. Restricted to the early Maeotian of the Eastern Paratethys Sea.

Eastern Paratethys. Early Maeotian (Late Miocene): Black Sea Lowland : Mykil’s’ke (Kherson Region); Berezneguvate, ravine Bila Krynytsya near Novorosiiske, Semenivka, (Mykolaiv Region, Ukraine) ( Ossaulenko, 1936); Crimea: Kerch, Semenovka ( Russia); Ciscaucasia : ravine Belaya Saklya, cape Popov Kamen’ (Krasnodar Krai, Russia);? Transcaspian Region: Cape Urdek (Mangystau Region, Kazakhstan) ( Iljina et al. 1976, hoc opus).