Tatara pseudosassia, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 153

Tatara pseudosassia n. sp.

Figs 33 B–E

Diagnosis. Elongate ranellid in shape with two strong columellar plaits and around 14 teeth on outer lip. Canal not very long.

Derivation of name. The name, which translates ‘False Sassia’, refers to its strong resemblance to Sassia faxense Ravn, 1933 in the same deposits.

Type material. The holotype, MGUH 33287 , is a nearly complete mould missing part of the aperture . Paratype MGUH 33288 was collected at Holtug, Stevns Klint , and comes from the same stratigraphic level as the holotype . Paratype MGUH 33289 is a mould of the aperture coming from the lithified top of the Højerup Member at Skeldervig, Stevns Klint .

Additional material. An external mould with the informal sample number SR.1123.A, and a fragmentary mould without number from the collections of the Natural History Museum of Denmark.

Type stratum and type locality. The lithified top of the Maastrichtian Højerup Member at Stevns Klint.

Occurrence. Lithified top of the Maastrichtian Højerup Member at Stevns Klint.

Description. Protoconch obtusely conical, composed of at least two smooth, not very convex whorls. Suture fairly weak.

Teleoconch elongated ranellid in outline with moderately convex whorls separated by distinct suture. Aperture elongated, taking up slightly more than half the shell height. Aperture width corresponding to 1/3 of its height. Parietal region with thin callus not completely covering underlying spiral ribs. Columella carrying two strong folds, the abapical one strongest. Denticles on the inner lip, if present, not preserved. Varices after old apertures fairly weak and thin, generally placed with a distance of half a whorl.

MGUH 33289, representing an internal mould of the aperture, has a wide and weakly convex outer lip carrying 14 evenly spaced small denticles at the inner margin. The small teeth decrease in size at the abapical end.

Teleoconch sculpture cancellate, consisting of thin spiral ribs and adapically slightly stronger transverse ribs, fading out on base. Spiral ribs numbering around 14 from adapical suture to beginning of canal, with between two and five on spire whorls. Transverse ribs very weakly sigmoid, at times slightly prosocline adapically, numbering around 20 per whorl on early whorls. Tubercles formed at connecting points between ribs. Growth lines nearly orthocline to slightly prosocline adapically.

Measurements. Protoconch poorly preserved, measuring between 0.75 and 1.2 mm in height and between 1.05 and 1.7 mm in width. Holotype specimen MGUH 33287 is 8.0 mm high and 4.8 mm wide, consisting of five whorls of which the last whorl lacks the basal part of the canal.

Remarks. Tatara pseudosassia n. sp. closely resembles the middle Danian Tatara danica Schnetler & Petit, 2006 from Faxe, Denmark, in the external sculpture and elongated ranellid shape, but differs by its slightly more compact shell outline, a higher number of teeth on the outer lip and seemingly by a slightly shorter canal.

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.