Claviscala minor, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 128

Claviscala minor n. sp.

Figs 29 O–Q

Diagnosis. Shell small; conical protoconch with around 35 opisthocyrt and strong collabral threads per whorl; teleoconch whorls rather weakly convex with weakly opisthocline transverse ribs and no spiral ribs or threads.

Derivation of name. Refers to the small size compared to the typical species of Claviscala .

Type material. The external mould MGUH 33236 consisting of the entire protoconch and first several teleoconch whorls is selected as holotype. Paratype MGUH 33237 is an external mould from the lithified top of the Højerup Member at Rødvig, Stevns Klint.

Additional material. ØSM.10042-354, six specimens with the informal sample numbers SR.808, SR.906, SR.996.A–B, SR.997.B–C, SR.1048 and SR.1065.B–C, and likely also SR.982, SR.1050 and SR.1051.A–B.

Type stratum and type locality. Lithified top of the Højerup Member of the Tor Formation exposed just south of Højerup Church, Stevns Klint .

Occurrence. This species is known exclusively from the lithified top of the upper Maastrichtian Højerup Member of the Tor Formation at Rødvig, just south of Højerup Church, and north of Kulsti Rende at Stevns Klint.

Description. Protoconch conical multispiral with four convex whorls, holotype 0.65 mm high and 0.4 mm wide. First protoconch whorl seemingly smooth, the following covered by up to around 35 closely spaced opisthocyrt collabral threads per whorl. Transition to teleoconch seemingly sharp, seen as a change in sculpture and a decrease in whorl expansion.

Teleoconch spire slender, conical with evenly increasing whorl width; initial whorl moderately convex, succeeding ones flattened, constricted just above narrow and relatively shallow abapical suture; whorl height corresponding to approximately 80 % of width. Transition to smooth flat base abrupt, marked by subperipheral carination. Aperture not known. Whorls carrying coarse, sharp and weakly opisthocline transverse ribs, their number increasing very slowly with growth from around 14 on first teleoconch whorl.

Measurements. The holotype MGUH 33236 is 2.9 mm high and at least 0.9 mm wide, consisting of four protoconch and five teleoconch whorls.

Remarks. Claviscala minor n. sp. is unusually small for this genus, but otherwise its features correspond quite well with the generic diagnosis. This species is easily distinguished from the Early Cretaceous Claviscala clementina ( Michelin, 1833) from France by the higher density of transverse ribs, which are also more transversely directed. It differs from the Late Cretaceous Claviscala sp. of Squires and Saul (2003a) from California by a slightly higher whorl convexity, a sharper transition to the base of the last whorl and the opisthocline nature of the transverse ribs. It differs from the Cretaceous Claviscala darwishi Abbass, 1963 from Egypt by the much less convex whorls.

Figures

FIGURE 29. A–B. Ageria skeldervigensis n. sp., Silicone cast of holotype MGUH 33226. Width 3.8, 4.5 mm respectively. C–E. Ageria laxa n. sp. C–D. Silicone cast of holotype MGUH 33227. Width 4.6 mm for teleoconch, 0.3 mm for protoconch. E. Silicone cast of paratype MGUH 33228. Width 6.7 mm. F–G. Ageria sp. F. Silicone cast of seemingly mislaid specimen MGUH 33229. Width 3.7 mm. G. Silicone cast of MGUH 33230. Width 0.6 mm. H–K. Coniscala umbilica n. sp. H. Silicone cast of paratype MGUH 33231. Width 1.4 mm. I–J. Holotype MGUH 33232. Width 19.6 mm. K. Paratype MGUH 33233. Width 12.4 mm. L–N. Opalia sp. L–M. Silicone cast of MGUH 33234. Width 1.3 mm. N. Silicone cast of MGUH 33235. Width 0.5 mm. O–Q. Claviscala minor n. sp. O–P. Silicone cast of holotype MGUH 33236. Width of teleoconch 0.9 mm. Width of protoconch 0.4 mm. Q. Silicone cast of paratype MGUH 33237. Width 1.3 mm. R. Claviscala sp., Silicone cast of MGUH 33238. Width 1.4 mm. S–V. Amaea aliceae n. sp. S–U. Silicone cast and inner mould of holotype MGUH 33239. Width 2.7, 2.0 and 3.1 mm respectively. V. Silicone cast of paratype MGUH 33240. Width 1.7 mm. W. Amaea stevniensis n. sp., Silicone cast of holotype MGUH 33241. Width 1.0 mm. X. Amaea sp. A. Silicone cast of MGUH 33242. Width of teleoconch 1.1 mm.