Brachystomia sp., Thivaiou, Harzhauser & Koskeridou, 2019

Thivaiou, Danae, Harzhauser, Mathias & Koskeridou, Efterpi, 2019, Early Miocene Gastropods from the Felli Section (Proto-Mediterranean Sea NW Greece), Geodiversitas 41 (8), pp. 323-366 : 352

Brachystomia sp.

(Fig. 8 B1, B2)

MATERIAL EXAMINED. — Sample F11: AMPG (IV) 2570-2572 (three specimens).

DIMENSIONS. — Maximum height: 2.00 mm.

DISTRIBUTION. — Early Miocene. Proto-Mediterranean Sea: Greece (this paper).

DESCRIPTION

Moderately slender shell with apical angle of c. 25°. Intorted type C protoconch of c. 210 µm diameter.Teleoconch consisting of five weakly convex smooth whorls; suture non-canaliculate impressed. Last whorl attains 60% of total height with faint angulation; base moderately convex, slowly contracting. Narrow ovate aperture; columella with small fold not visible in direct apertural view. Umbilicus reduced to barrow chink.

REMARKS

The apex appears blunt due to the completely intorted protoconch which is a character separating the genera Brachystomia Monterosato, 1884 and Odostomia Fleming, 1813 ( Robba 2013; Landau & LaFollette 2015). Furthermore, the shell is smooth and the protoconch very flat which are characters shared with the type species of the genus B. scalaris MacGuillivray, 1843 as described and illustrated by HØisaeter (2014). Based on the similarities The shape of the Greek shells share the basic characters of the genus Brachystomia Monterosato, 1884 Odostomia (Brachystomia) sp. from the Miocene of the North Sea Basin ( Moths et al. 2010). It has an intorted protoconch, a smooth shell, and similar aperture with a narrow umbilical chink and a columellar tooth not clearly visible in direct apertural view. Nevertheless, the latter specimen has a less blunt apex and is slightly longer (maximum height: 2.40 mm) than the Greek specimen. The general aspect and morphology is also close to Odostomia fusulus Monterosato, 1878 ( Landau et al. 2013) (= Auristomia fusulus (Monterosato, 1878)) , including the structure of the protoconch, but it is narrower and has a smaller aperture. Odostomia elisabethae Boettger, 1907 from the Serravallian of the Karaman Basin ( Turkey) is another morphologically close species with a less intorted protoconch, clearly defined umbilicus, much more prominent umbilical fold, and smaller aperture than the Greek specimen. Lastly, the overall morphology is close to Ondina cicatricosa Lozouet, Lesport & Renard, 2001, especially regarding the apex and the proportion of the last whorl, the main differences with the Greek specimen are the opisthocline growth lines, the inconspicuous spiral sculpture which is absent from Brachystomia sp., and the deep umbilicus.

Figures

FIG. 8. — A1, A2, ‘Odostomia’ sp. 2, AMPG(IV) 2558; B1-B3, Megastomia sp. 1, AMPG(IV) 2560; C1, C2, Brachystomia sp., AMPG(IV) 2570; D1-D3, Megastomia sp. 2: D1, AMPG(IV) 2563;D2, D3, AMPG(IV) 2564;E1-E4, Pyramistomia aliakmoni n. sp.: E1, E2, holotype, AMPG(IV) 1500;E3, paratype 1, AMPG(IV) 1501 (SEM image); E4, AMPG(IV) paratype 1, AMPG(IV) 1501, protoconch (SEM image); F1-F4, Parthenina sp. 1: F1, F2, AMPG(IV) 1573; F3, AMPG(IV) 1574 (SEM image); F4, AMPG(IV) 1574, apex (SEM image); G1, G2, Parthenina sp. 2: G1, AMPG(IV) 2575; G2, AMPG(IV) 2575, apex (SEM image); H,?Syrnola sp., AMPG(IV) 2577 (SEM image). Scale bars: A1, A2, B1-B3, D1, G1, H, 500 µm; C1, C2, D2, D3, E1, E2, 1 mm; E3, F1, F2, 400 µm; E4, F3, 200 µm; F4, G2, 100 µm.