Arene jakobseni, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 77-78

Arene jakobseni n. sp.

Figs 22 R–U, 23A

Diagnosis. Shell relatively high; planispirally coiled protoconch featuring convex whorls; teleoconch with three to four strong, beaded spiral cords above whorl periphery.

Derivation of name. In honour of Sten Lennart Jakobsen, conservator at the Geological Museum of Copenhagen, who has been a tremendous help to this project.

Type material. Holotype MGUH 33119 is a natural external and internal mould of the spire . Paratype MGUH 33120 is an external mould of the base and aperture from Holtug Quarry, possible from one of the Korsnaeb Member infilled Thalassinoides burrows in the Cerithium Limestone Member , but the gastropod is filled out with material from the Cerithium Limestone .

Type stratum and type locality. Lower Danian Cerithium Limestone Member at Holtug Quarry, Stevns Klint .

Occurrence. Lower Danian Cerithium Limestone Member of the Rødvig Formation at Holtug Quarry, Stevns Klint.

Description. Shell relatively high with planispirally coiled protoconch. Protoconch 1.6 mm wide, consisting of 2 smooth or weakly transversely striated and slightly depressed whorls. Teleoconch turbiniform with deeply impressed sutures and strongly convex whorls; a weak keel may be present; base of shell weakly flattened with deep, but narrow umbilicus. Aperture circular with thick and smooth, flattened lip and low varix. Teleoconch surface heavily sculptured with eight to ten beaded or spiny spiral cords, three to four strong cords on adapical side, one at the periphery and the rest, which generally are much finer and more closely spaced, on the base. Spiny tubercles hollow in growth direction; restricted to primary three spiral ribs. Spiral cords on base decreasing in strength towards umbilicus, which is bounded by a single more strongly developed beaded spiral rib. Cords crossed by very fine and densely spaced transverse striae.

Measurements. Holotype MGUH 33119 is 9.2 mm high and 8.6 mm wide.

Remarks. Arene jakobseni n. sp. differs from the Campanian A. mcleani Kiel & Bandel, 2002a from Spain and the Maastrichtian A. truncatospaera Sohl, 1998 from Jamaica in the sparser and spinier sculpture and the more strongly convex whorls. It closely resembles the middle Danian Arene depressa ( Ravn, 1933) from Denmark, but differs by the distinctly larger size, the coarser and sparser teleoconch sculpture and possible by a narrower umbilicus, though this may relate to ontogeny.

Figures

FIGURE 22. A. Phorcus sp., Silicone cast of MGUH 33109. Exposed width 2.2 mm. B–C. Stomatella sp., External mould of MGUH 33110. Figure B has been colour inverted and mirrored to show it in positive. Width 1.5 mm. D–F. Solariella sp. D–E. Silicone cast of MGUH 33111. Width 6.2 mm. F. Silicone cast of aperture of MGUH 33112. Width 5.95 mm. G–I. Skenea sp. G–H. Inner mould of MGUH 33113. Width 5.2 mm. I. Inner mould of MGUH 33114. Width 10.2 mm. J–K. Leucorhynchia sp., Silicone cast of MGUH 33115. Width 2.4 mm. L–N. Tectus? indecorus n. sp., L. Umbilical view of inner mould of paratype ØSM.10042-327-b. Width 19.7 mm. M–N. Silicone cast of holotype MGUH 33116. Width 1.7 mm. O–P. Homalopoma sp., Silicone cast and inner mould of MGUH 33117. Width 9.6, 6.9 mm respectively. Q. Calliomphalus (Calliomphalus) sp., Silicone cast of MGUH 33118. Width 3.1 mm. R–U. Arene jakobseni n. sp. R–T. Silicone cast of holotype MGUH 33119. Width 8.6 mm. U. Silicone cast of paratype MGUH 33120. Width of aperture 4.8 mm.