Acmaea selandica, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 56

Acmaea selandica n. sp.

Figs 19 A–C

Diagnosis. Broadly oval Acmaea shell with height less than 20 % of length and a pointed apex situated 25–35 % of shell length from anterior margin. Shell surface smooth or with scattered weak radial striation.

Derivation of name. Refers to the Danish island Sealand on which it is found.

Type material. Holotype MGUH 33077 from Skeldervig at Stevns Klint, and paratypes MGUH 33078 from Bøgeskoven and MGUH 33079 from the cliff just north of Holtug Bay, both localities at Stevns Klint. All three specimens belong to the uppermost part of the Maastrichtian Tor Formation.

Additional material. At least one and probably two specimens from Rødvig. Furthermore a specimen with shell, ØSM.10042-199-a with counterpart in ØSM.10042-191 is found in the collection of Østsjaellands Museum. This is also from Rødvig.

Type stratum and type locality. Upper part of the upper Maastrichtian Tor Formation at Skeldervig, Stevns Klint, Denmark .

Occurrence. Uppermost Tor Formation at Stevns Klint.

Description. Shell low, height corresponding to less than 20 % of length, broadly oval with cone-shaped apex situated 25–35 % of shell length from anterior margin. Surface of shell smooth or with scattered radial striation interrupted by moderately coarse, irregular growth lines. Interior surface with indistinct wide muscle imprint, narrowing in front of apex; widest part of imprint on posterior part of shell approximately 17 % of shell length.

Measurements. Largest shell, holotype MGUH 33077, 6.0 mm long and 5.4 mm wide.

Remarks. Acmaea selandica n. sp. differs from the Danian A. simplex ( Briart & Cornet, 1887) from Belgium by the relatively lower shell with its slightly more anterior apex and from the Belgian A. hannonica ( Vincent, 1930) of the late Maastrichtian, the Palaeocene Acmaea sp. 1 and Acmaea sp. 2 described by Kollmann & Peel (1983) from Greenland and A. rigida Kaunhowen, 1898 from Maastricht by the smoother surface. This species is distinguished from A. laevigata Binkhorst, 1861 by the very low shell and from Acmaea sp. 3 sensu Kollmann & Peel (1983) from the Palaeocene of West Greenland by the more pointed and slightly curved aperture. It is distinguished from the Maastrichtian A. ciplyana ( Ryckholt, 1852) of Ciply, Belgium, by the lack of the very fine and dense striae covering the surface of the latter and from the Palaeocene A. poulseni Ravn, 1939 of Denmark by the less convex and smoother shell. Acmaea selandica n. sp. is rather close to Acmaea ? sp. sensu Kollmann & Peel (1983) from which it mainly appears to differ by the strong effacement of growth-lines.

Figures

FIGURE 19. A–C. Acmaea selandica n. sp. A. Inner mould of holotype MGUH 33077. Length 5.9 mm. B. Paratype MGUH 33078. Length 2.6 mm. C. Internal mould of paratype MGUH 33079. Length 4.45 mm. D–E. Acmaea? sp. Wax cast of now lost specimen MGUH 33080. Length 19.7 mm. F–G. Cocculina? sp. Silicone cast of MGUH 33081. Exposed length 5.7 mm. H. Symmetrocapulus? sp., external mould MGUH 33082. Length 2.4 mm. I–K. Emarginula coralliora Lundgren, 1867. I–J. Silicone cast of MGUH 33083. Length 2.9 mm, height 1 mm. K. Inner mould of MGUH 33084. Length 7.8 mm. L–Q. Cranopsis cretacea n. sp. L–O. Silicone cast and inner mould of holotype MGUH 33085. Length 3.6 mm, width 2.6 mm. P–Q. Silicone cast and inner mould of paratype MGUH 33086. Length 2.1 mm. R–S. Palaeoloxotoma sp., Silicone cast of MGUH 33087. Length 17.2 mm.