Ravniella danica ( Ravn, 1902 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 161

Ravniella danica ( Ravn, 1902)

Figs 34 J–N

1902 Cinulia danica n. sp. Ravn: 238–239, pl. III, fig. 7.

1970 Tornatellaea (Ravniella) danica (Ravn) —Rosenkrantz: 431–433, fig. 10: 1.

Diagnosis. Protoconch heterostrophic, of 1½ smooth whorls. Teleoconch low-spired with strongly developed columellar folds and around eight teeth on outer lip. Whorl sculpture of widely spaced, finely pitted spiral grooves, generally numbering three to five on spire whorls.

Type stratum and type locality. Cerithium Limestone Member at Stevns Klint , Denmark .

Material. Of the original 12 type specimens Ravn (1902) used for his description, only the one figured, MGUH 126, is known today. The others were not given a number and are no longer possible to separate from the rest of the specimens found in the old collections. For this reason MGUH 126 is here selected as lectotype. Additional material consists of MGUH 33302, MGUH 33303, ØSM.10042-88-a–b, ØSM.10042-89-a–b, ØSM.10042-106, more than 130 specimens without numbers from the old collections at the Geological Museum, Natural History Museum of Copenhagen, and 43 new specimens with the informal sample numbers SH.106.B, SH.142, SH.148, SH.161, SH.186, SH.197.A, SH.205, SH.206, SH.285.A–B, SH.285.A, SH.289 (2 specimens), SH.290, SH.303. A (2 specimens), SH.324, SH.325.B–C, SH.325.C, SH.334.A–B, SH.334.C, SH.352.A–B (6 specimens), SH.384. A, SH.410.A–B, SH.414.B–C, SH.416, SH.418.A–B, SR.168, SR.225, SR.278, SR.283, SR.286, SR.307.A–B, SR.400, SR.516 (2 specimens), SR.570.A–C, SR.642.B, SO.110.A–B, DN.26.A–B, DN.30.A–B, DN.33.A–B (2 specimens) and DN.52.A–B.

Occurrence. Common in the Cerithium Limestone Member at Stevns Klint and in the contemporaneous ‘dead layer’ in Northern Jutland.

Description. Shell subovate, small, generally below 10 mm high, width/height ratio varying between 57 and 70 %, generally decreasing with size. Protoconch heterostrophic with nearly 1.5 loosely coiled, smooth whorls. Transition to teleoconch sharp, marked by appearance of spiral grooves. Protoconch between 0.6 and 0.8 mm wide. Teleoconch with rather weakly convex whorls and distinct suture. Spire sides nearly straight to at times slightly concave due to an increase in whorl expansion on later whorls. Last whorl corresponding to between 75 and 85 % of shell height. Aperture narrowly oval-rhombic, width approximating 2/3 the height. Inner lip with two widely spaced, oblique strong columellar folds and a weaker parietal fold slightly above columella. Outer lip moderately sharp, slightly thickened, carrying around eight sharp teeth, although adapical and abapical ones often appears effaced or missing. Whorl sculpture of widely spaced, finely pitted spiral grooves, generally numbering three to five on spire whorls, adapical groove markedly stronger than succeeding ones. Last whorl typically with around 15 spiral grooves.

Measurements. Lectotype MGUH 126 is approximately 6.5 mm high and 4.3 mm wide, consisting of 5 ½ whorls.

Remarks. This gastropod, which most likely was a vermivore ( Jeffery & Tracey 1997), is one of the more dominant gastropod species in the Cerithium Limestone Member , although it generally does not exceed 2 % of the total number of gastropod specimens.

Figures

FIGURE 34. A–E. Admetula sp. A–D. Silicone cast and internal mould of MGUH 33297. Widths 6.6, 7.2, 7.0 and 6.1 mm respectively. E. Internal mould of MGUH 33298. Width 5.6 mm. F. Kroisbachia sp., Silicone cast of MGUH 33299. Width 2.4 mm. G. Mataxa s.l. sp., Silicone cast of MGUH 33300. Width 3.9 mm. H–I. Neogastropoda genus et sp. indet., Silicone cast of MGUH 33301. Width 0.7 mm. J–N. Ravniella danica (Ravn, 1902). J–K. Silicone cast of MGUH 33202. Widths 4.7 and 4.3 respectively. L. Silicone cast of lectotype MGUH 126. Width 4.3 mm. Photograph by S.L. Jakobsen. M–N. Silicone cast of MGUH 33303. Width 4.1 and 3.8 mm. O–S. Disculus selandicum (Ravn, 1902). O. Silicone cast of MGUH 33304. Width 8.7 mm. P–Q. Silicone cast of paralectotype MGUH 80 figured by J.P.J. Ravn (1902, Pl. I: 6). Width 7.1, 6.9 mm respectively. R. Silicone cast of lectotype MGUH 79. Width 6.0 mm. Photograph by S.L. Jakobsen. S. Silicone cast of MGUH 33305. Width 5.9 mm.