Ageria skeldervigensis, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 111-112

Epetrium s.l. skeldervigensis n. sp.

Figs 27 P–R

Diagnosis. Very slender shell with sigmoid collabral threads and no spiral sculpture on protoconch whorls and with opisthocline, truncated transverse ribs on early teleoconch whorls.

Derivation of name. Refers to the type locality at Skeldervig, Stevns Klint.

Type material. Holotype MGUH 33194 is a nearly complete specimen preserved as an external mould . Paratype MGUH 33195 comes from the same stratum as the holotype and was collected at Holtug Quarry, Stevns Klint . Paratype MGUH 33196 is from the Cerithium Limestone Member at Skeldervig, Stevns Klint .

Additional material. An external mould from Holtug is deposited in the uncatalogued old collections at the Natural History Museum of Denmark.

Type stratum and type locality. Cerithium Limestone Member of the Rødvig Formation at Skeldervig, Stevns Klint.

Occurrence. Lower Danian Cerithium Limestone Member of the Rødvig Formation at Skeldervig and Holtug Quarry. Lower Danian Korsnaeb Member north of Holtug at Stevns Klint.

Description. Protoconch planktotrophic with around 2 ½ moderately to weakly convex whorls; protoconch height approximately 0.4 mm and width 0.3 mm. Sculpture on embryonic shell unknown. Last protoconch whorl carrying approximately 14 fairly coarse, slightly sigmoid collabral threads, the main adapical part opisthocyrt with a more sharply prosocyrt curvation at abapical suture. Spiral threads absent. Transition to teleoconch not visible.

Spire slender turriform, sinistrally coiled, the first two teleoconch whorls seemingly smooth and moderately to weakly convex. Succeeding whorls flattened with sharp to later more gradual transition to base; whorl height corresponding to less than half the width. Base strongly flattened on early teleoconch whorls, becoming more convex with growth. Aperture relatively small, narrow with straight and smooth columella carrying large columellar and parietal lip. Outer lip slightly thickened. Canal not visible or preserved. Growth lines fine, opisthocline, nearly straight and densely distributed.

Teleoconch sculpture consisting of 18 to around 26 opisthocline transverse ribs per whorl and wide and somewhat effaced spiral ribs and furrows. Transverse ribs only distinct on abapical two spiral ribs of early whorls; fading out before completely disappearing on later whorls. Spiral sculpture composed of two narrow and low spiral ribs abapically, divided by shallow furrow and succeeded adapically by moderately deep spiral furrow situated on abapical half of whorl. Adapical part of whorl carrying two wide and indistinct spiral bands divided by weak spiral furrow. Whorl base characterized by eight or more weak and closely lying spiral ribs, becoming fainter towards columella.

Measurements. Holotype MGUH 33194 is 9.6 mm high and 2.4 mm wide, consisting of 20 whorls (protoconch included).

Remarks. The pronounced opisthocline axial sculpture with well developed, though truncated transverse ribs may indicate that the Danish taxon from the Cerithium Limestone Member most likely does not belong to this genus sensu stricto. The material, though, is too poor for the erection of a new genus and the taxon is at the moment assigned Epetrium sensu lato.

Epetrium s.l. skeldervigensis n. sp. is clearly distinguished from the slightly younger Epetrium ? cretacea Ravn, 1933 and E.? crassigranulata Ravn, 1933 from Denmark by the more abapical location of the beaded spiral ribs, which are less strongly developed and by the different protoconch sculpture lacking spirals. It differs from the Danian E.? separabilis Ravn, 1933 from Denmark, by the lack of axial sculpture and beading on late teleoconch whorls and seemingly slightly lower and wider spiral ribs. It is characterized from the late Maastrichtian ‘ Triforis’ cincta Kaunhowen, 1898 from Holland by the presence of axial sculpture. It seems closely related to the Danish middle Danian Triphoridae gen. et sp. indet. 2 sensu Lauridsen & Schnetler (2014: p. 75), and they may actually be conspecific. At present the material is too limited for a closer comparison.

Figures

FIGURE 27. A–B. Melanella? sp., Silicone cast of MGUH 33183. Width 1.4 mm. C–E. Vermetus sp., C. Silicone cast of attached tube MGUH 33184. Largest diameter 6.6 mm. D. Inner mould of protoconch and initial teleoconch inside bryozoan ball. MGUH 33185. Protoconch 0.5 mm wide. E. Silicone cast of MGUH 33186. Width 3.5 mm. F–J. Thylacodes contendis n. sp. F. Attached holotype mould MGUH 33187. Width 2.4 mm. G–H. Silicone cast of paratype MGUH 33188. Width 2.9 mm. I. Silicone cast of paratype MGUH 33189. Width 3.0 mm. J. Silicone cast of free whorl paratype MGUH 33190. Tube diameter 1.8 mm. K–M. Thylacodes? sp., Silicone cast of MGUH 33191. Width 2.4 mm. N. Dendropoma sp., Protoconch and initial teleoconch tube of MGUH 33192. Width 1.7 mm. O. Laxispira sp., Silicone cast of MGUH 33193. Width 3.6 mm. P–R. Epetrium s.l. skeldervigensis n. sp. P. Silicone cast of holotype MGUH 33194. Width 2.4 mm. Q. Silicone cast of paratype MGUH 33195. Width 4.0 mm. R. Silicone cast of paratype MGUH 33196. Width 3.6 mm. S. Triphoridae genus et sp. indet. Sinistrally coiled protoconch MGUH 33197. Width 0.7 mm. T–W. Cerithiopsis restemlongis n. sp. T. Silicone cast of holotype MGUH 33198. Width 1.0 mm. U. Silicone cast of paratype MGUH 33199. Width 1.5 mm. V. Silicone cast of paratype protoconch MGUH 33200. Width 0.5 mm. W. Silicone cast of paratype protoconch MGUH 33201. Width 0.6 mm and height 1.1 mm. X. Cerithiopsis? sp., Silicone cast of MGUH 33202. Width 0.6 mm. Y–AE. Thereitis carlsbergi n. sp. Y–Z. Silicone cast of holotype specimen MGUH 33203. Width of protoconch 0.6 mm and teleoconch 1.4 mm. AE. Silicone cast of paratype MGUH 33204. Width 0.7 mm.