Megastomia sp. 1, Monterosato, 1884

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

Megastomia sp. 1

(Fig. 8 B1-B3)

MATERIAL EXAMINED. — Sample F11: AMPG ( IV) 2560-2562 (three specimens).

DIMENSIONS. — Maximum height: 1.20 mm.

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

DESCRIPTION

Small, solid shell with broad conical outline; spire angle c. 26°. Intorted type C protoconch of c. 300 µm diameter, resulting in very blunt apex. Axial sculpture consisting of inconspicuous, orthocline growth lines. Whorls only faintly convex, sutures impressed and linear. Last whorl inconspicuously angular at periphery; accounting for about 60% of total height. Columella weakly concave with central columellar tooth; outer lip smooth. Six elongate teeth appear behind aperture in last whorl. Umbilicus reduced to narrow chink.

REMARKS

The generic placement is based on the presence of elongate teeth behind the outer lip ( Peñas & Rolán 1999; Robba 2013). All available specimens are very small and might represent subadult specimens. The type C protoconch distinguishes this species from the widespread Miocene to Recent European Megastomia conoidea ( Brocchi, 1814) . Among the Recent species of Megastomia , only M. lorioli (Hornung & Mermod, 1924) develops a type C protoconch ( Bogi & Cuneo 1999). This Lessepsian migrant differs from the Aquitanian species from Greece in its strongly incised suture. The extant Odostomia lukisii Jeffreys, 1859 has a very similar shell morphology, with an immersed type C protoconch, but lack the teeth within the outer lip.

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.