Ceritella convexa, Gründel & Keupp & Lang & Nützel, 2022

Gruendel, Joachim, Keupp, Helmut, Lang, Fritz & Nuetzel, Alexander, 2022, Late Jurassic (Upper Kimmeridgian) Heterobranchia (Gastropoda) of the coral-facies of Saal near Kelheim and the viciniy of Nattheim (Germany), Zitteliana 96, pp. 179-221 : 179

Ceritella convexa sp. nov.

Plate 4: figs 1-5

Derivatio nominis.

Lat. Ceritella convexus - convex; for the convex, somewhat inflated whorls.

Holotype.

SNSB-BSPG 2021 XV 9, collection Lang.

Locus typicus.

Quarry Saal near Kelheim.

Stratum typicum.

Upper Kimmeridgian.

Paratypes.

Twenty-two mostly juvenile specimens from Saal (collection Lang) SNSB-BSPG 2021 XV 8, 147-167.

Additional material.

Three specimens from Saal, without type status (collection Lang).

Diagnosis.

Shell broadly fusiform; whorls with distinctly oblique ramp; larger specimens have a somewhat inflated last whorl; early whorls with axial ribs changing to strengthened growth lines in later whorls; ribs curve backward below ramp edge; spiral cords absent.

Description.

A large specimen is 4.3 mm high. The shell is broadly oval, fusiform with an acute spire. The shell width is variable. Larger specimens have a somewhat inflated last whorl. The sutures are distinct. The whorls have a relatively broad, strongly oblique ramp, demarcated from whorl face by an edge. The spire whorls are broad and low. The early whorls have opisthocline axial ribs which weaken during ontogeny and finally change to strengthened growth lines. The ribs or strengthened growth lines run prosocyrt opisthocline from edge near ramp to base, and curve strongly backward at the edge that demarcates the ramp. The course of the growth lines is not visible on the ramp. Spiral ornament is absent. The base is strongly convex and smooth except of growth lines. The aperture is narrow and acute adapically. It has a short, oblique siphonal canal.

Relationships.

Ceritella pupoides ( d’Orbigny) sensu Fischer and Weber (1997) is slenderer, has a higher spire, and lacks axial ribs. Ribs are also absent in Ceritella lauretana Guirand and Ogérien, C. dolium Loriol (both sensu Cossmann 1895), Orthostoma granum Loriol in Loriol and Pellat (1866), and Acteonina lauretana Guirand and Ogérien sensu Loriol in Loriol and Bourgeat (1886-1888). Acteonina terebra Étallon sensu Loriol in Loriol and Bourgeat (1886-1888) is slenderer, lacks an oblique ramp, has a higher spire and its axial ribs are not reduced during ontogeny. Ceritella (Ceritellopsis) parvula (F. A. Roemer) sensu Huckriede (1967) has a horizontal ramp and therefore a gradate spire; it has fewer axial ribs that are stronger and not bent backward adapically.

Figures

Plate 4. (1 - 5) Ceritella convexa sp. nov. (1 - 2) Paratype, SNSB-BSPG 2021 XV 8, Saal (collection Lang), lateral views, height 4.3 mm. (3 - 5) Holotype, SNSB-BSPG 2021 XV 9, Saal (collection Lang); (3 - 4) lateral views, height 3.5 mm; (5) apical view, width 1.8 mm. (6 - 8) Ceritella sp. 1, SNSB-BSPG 2021 XV 7, Saal (collection Lang); (6 - 7) lateral views, height 3.2 mm; (8) apical view, width 1.3 mm.