Turbonilla s.l. sp. 2, Risso, 1826

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 : 356

Turbonilla s.l. sp. 2

(Fig. 9 B1-B3)

MATERIAL EXAMINED. — Sample F11: AMPG ( IV) 2583 (one specimen).

DIMENSIONS. — Maximum height: 2.58 mm (incomplete), diameter: 1.00 mm.

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

DESCRIPTION

Type A2 helicoidal protoconch of three whorls forming angle of 125° relative to shell axis; diameter: 360 µm. Last whorl disproportionately larger than the first two. Fragmentary teleoconch consisting of 4.5 convex whorls with incised suture; spire angle about 20°. Sculpture consisting of blunt, faintly opisthocline to sigmoidal axial ribs with convex tops. Spacing slightly irregular with smooth, moderately deep interspaces. Each whorl bears two varix-like axial ribs; first and second one placed under the tip of the protoconch and on opposite side. No spiral sculpture. Aperture missing.

REMARKS

This species of Turbonilla is characterized by its convex whorls, the prominent sculpture with two varix-like axial ribs per whorl and the allometric growth of the last protoconch whorl. Turbonilla koeneniana Sacco, 1892 as figured by A.W. Janssen (1984) from the Miocene of the Netherlands is a closely similar species, which differs by having more convex whorls, a slightly more conical shape and randomly placed varices of variable width. Nevertheless, the protoconch has a similar structure with a very inflated last whorl. The different varieties of T. pseudocostellata with prominent costae presented by Sacco (1892) differ from the present specimen by having more rounded ribs, no varices, more slender shape, less prominent protoconch and less impressed sutures.

Figures

FIG. 9. — A1-A3, Turbonilla (s.l.) sp. 1, AMPG(IV) 2580; B1-B3, Turbonilla (s.l.) sp. 2, AMPG(IV) 2583; C1, C2, Turbonilla (s.l.) sp. 3, AMPG(IV) 2584; D1-D3, Turbonilla (s.l.) sp. 4: D1, AMPG(IV) 2586 (SEM image); D2, D3, AMPG(IV) 2687. Scale bars: 500 µm.