Unitas heinbergi, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 156-157

Unitas heinbergi n. sp.

Figs 33 O–R

Diagnosis. Protoconch conical with 2 ¾ whorls. Anterior canal of teleoconch moderately long and shallow. Sculpture moderately coarse with around 16 transverse ribs per whorl and four spiral ribs.

Derivation of name. In honour of Claus Heinberg, who has been of great help with the initial field work and discussions on the palaeo-environment during the deposition of the Cerithium Limestone Member.

Type stratum and type locality. The holotype was collected 50 to 60 centimetres above the Cretaceous-Palaeogene boundary (= the P1b planktonic foraminifer zone), corresponding to the top of the Cerithium Limestone Member at Flagbanken, Stevns Klint.

Type material. The holotype MGUH 33295 is a nearly complete internal and external mould . Paratype MGUH 33296 is an internal and external mould from the Cerithium Limestone Member just north of the Holtug Quarry .

Occurrence. Unitas heinbergi n. sp. is known from the Cerithium Limestone Member north of Holtug Quarry and from the P1b planktonic foraminifer zone 50 to 60 centimetres above the Cretaceous-Palaeogene boundary, corresponding to the top of the Cerithium Limestone Member at Flagbanken, Stevns Klint.

Description. Protoconch conical with a somewhat flattened or planispiral apex and consisting of 2 ¾ flattened to later convex whorls. Initial whorls smooth, while last half whorl has three weak spiral threads. Suture moderately deep. Protoconch measuring about 1.2 mm in height and 1.3 mm in width. Transition to teleoconch marked by the appearance of strong transverse ribs.

Teleoconch slender fusiform with adapically convex whorls separated by deep suture. Spire whorls twice as wide as high. Base less convex, ending in wide canal. Aperture elongated oval in outline, abapically reaching out into moderately long and shallow canal. Columella deflected slightly to the left, with two moderately strong adapical folds and a much weaker abapical fold. Callus moderately thick and wide on parietal region. Outer lip with low varix and seven rounded teeth at an even distance from each other; the abapical one much weaker than others.

Teleoconch sculpture dominated by sharp and strong, moderately prosocline transverse ribs numbering around 16 per whorl. Ribs fading out at transition to canal. The transverse ribs are crossed by around four weaker spiral ribs on spire whorls, forming sub-reticulate pattern. Base and especially canal more dominated by spiral ribs. Unevenly distributed and thin varices occur throughout.

Measurements. Holotype MGUH 33295 approximately 5.2 mm high and 3.0 mm wide, consisting of protoconch and two teleoconch whorls.

Remarks. Unitas heinbergi n. sp. differs from the Danian Unitas malaisei ( Briart & Cornet, 1877) from Belgium by the higher number of transverse ribs per whorl, the longer anterior canal and the more adapical location of the central columellar fold relative to the columellar termination. It differs from the middle Danian Unitas anderseni Schnetler & Petit, 2006 and U. aliceae Schnetler & Petit, 2006 from Faxe, Denmark, by the distinctly less elongated teleoconch outline with its coarser sculpture. It appears very closely related to the Palaeocene (Selandian) U. scalata Traub, 1989 from Germany, but differs by a less convex whorl outline and a larger protoconch.

Figures

FIGURE 33. A. Mangeliid genus et sp. indet., Silicone cast of MGUH 33286. Protoconch width 0.8 mm. B–E. Tatara pseudosassia n. sp. B–C. Silicone cast of holotype MGUH 33287. Width 4.8 mm. D. Silicone cast of paratype MGUH 33288. Width 3.7 mm. E. Internal mould of last whorl of paratype MGUH 33289. Width 5.9 mm. F–H. Tatara sp., Silicone cast and internal moulds of MGUH 33290. Widths 10.4, 9.9 and 9.9 mm respectively. I–L. Sveltella sp. I–J. Silicone cast of MGUH 33291. Width of teleoconch 3.0 mm. Width of picture J 3.5 mm. K–L. Silicone cast of MGUH 33292. Widths 3.1 mm. M–N. Babylonella sp. M. Silicone cast of MGUH 33293. Width 1.6 mm. Picture by S.L. Jakobsen. N. Silicone cast of MGUH 33294. Width 1.7 mm. O–R. Unitas heinbergi n. sp. O–Q. Silicone cast of holotype MGUH 33295. Widths 3.0, 3.0 (vertical on figure) and 2.8 mm respectively. R. Silicone cast of paratype MGUH 33296. Width 2.9 mm.