Opaliopsis carlsbergi, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 134-135

Opaliopsis carlsbergi n. sp.

Figs 30 I–K

Diagnosis. Shell profile largely unchanged from protoconch to teleoconch; protoconch high-spired with approximately 30 collabral ribs; teleoconch with 15 to 17 relatively low and sharp transverse ribs and no spiral ribs.

Derivation of name. In honour of the Carlsberg Foundation for its financial support of this work.

Type material. Holotype MGUH 33248 is an external mould with well preserved details, while paratype MGUH 33249 from the same locality and horizon is a nearly complete external mould with slightly poorer preservation of details . Paratype MGUH 33250 is a nearly complete mould from the same strata and locality as the holotype .

Additional material. In addition to the type material another five external moulds from the same locality and horizon were examined (Informal sample numbers SR.747, SR.982, SR.1052, SR.1122 (2 specimens )) .

Type stratum and type locality. Lithified top of the upper Maastrichtian Højerup Member of the Tor Formation at Rødvig, Stevns Klint .

Occurrence. Lithified top of the Maastrichtian Tor Formation at Rødvig, Stevns.

Description. Protoconch consisting of four convex whorls, widening rather rapidly, the last measuring 0.3 millimetres in width. Initial whorl apparently smooth. Succeeding whorls carrying up to in excess of 30 opisthocline and slightly opisthocyrt collabral ribs reaching from suture to suture. Transition to teleoconch sharp, marked by decreasing whorl expansion and a shift from fine collabral ribs to coarse transverse ribs.

Teleoconch spire high and narrow with low, convex whorls; whorl height corresponding to 2/3 the width. Transition to flattened base marked by clear angle; weakly developed subsutural collar may be present. Aperture ovoid with concave columella with callus.

Teleoconch sculpture consisting of 15 to 17 strong and moderately sharp varix-like transverse ribs per whorl. Aperture unknown.

Measurements. Paratype specimen MGUH 33250 is 3.0 mm high and at least 0.8 mm wide with two preserved protoconch and eight teleoconch whorls.

Remarks. Opaliopsis carlsbergi n. sp. resembles the Campanian Opaliopsis faearium ( Dockery, 1993) , but differs in having a more high-spired protoconch with a width less than half that of the latter. It is clearly distinguished from the Maastrichtian O. aff. faearium sensu Nützel (1998) from the USA by the much coarser collabral ribs on the protoconch, which are also less opisthocyrt. Opaliopsis carlsbergi n. sp. differs furthermore from the Albian O. aff. dupinianum ( d’Orbigny, 1842) sensu Kiel (2006) from Madagascar by the lack of spiral ribs and by a more even transition from protoconch to teleoconch with regard to shell outline. It also resembles the Albian Opaliopsis franciscae ( Collignon, 1949) , but differs in the absence of spiral ribs and the higher number of transverse ribs on the first teleoconch whorl, which only reach ten on O. franciscae (see Kiel 2006: p. 463). The slightly younger middle Danian limestone deposits of Denmark include the species Graphis danica Ravn, 1933 and Graphis sp. 1 sensu Lauridsen & Schnetler (2014: p. 71). They closely resemble Opaliopsis carlsbergi n. sp., but may be differentiated on strength of the protoconch, which is smooth and paucispiral, lacking the fine collabral ribs characterizing Opaliopsis .

Figures

FIGURE 30. A–B. Amaea sp.A. Details of protoconch on external mould of MGUH 33242 shown in natural view and mirrored with inverted colours. Width of protoconch 0.6 mm. C–D. Amaea sp. B. C. Silicone cast of protoconch MGUH 33243. Width 0.6 mm. D. Silicone cast of protoconch MGUH 33244. Width 0.4 mm. E. Amaea? sp. C, Silicone cast of ØSM.10042-373. Width 5.5 mm. F–G. Acirsa torensis n. sp. F. Silicone cast of holotype MGUH 33245. Width 0.8 mm. G. Silicone cast of paratype MGUH 33246. Width 1.1 mm. H. Acirsa sp., Silicone cast of MGUH 33247. Height 6.2 mm. I–K. Opaliopsis carlsbergi n. sp. I. Silicone cast of holotype MGUH 33248. Height 2.2 mm. J. Silicone cast of paratype MGUH 33249. Height 1.7 mm. K. Silicone cast of paratype MGUH 33250. Height 3.0 mm. L–M. Fusinus schnetleri n. sp. L. Silicone cast of holotype MGUH 33251. Height 23.9 mm. M. Silicone cast of paratype MGUH 33252. Height 13.4 mm. N–O. Streptochetus sp. A. Silicone cast of MGUH 33253. Width of figure N 2.7 mm. Width of teleoconch 3.5 mm. P–Q. Streptochetus? sp. B. Silicone cast of MGUH 33254. Teleoconch width 2.6 mm.Width of protoconch 0.6 mm. R–T. Latirulus? sp. R–S. Silicone cast of MGUH 33255. Width of protoconch 0.7 mm. Height of teleoconch 10.5 mm. T. Silicone cast of MGUH 33256. Width 3.7 mm. U–W. Dolicholatirus lorenzi n. sp. U. Silicone cast of holotype MGUH 33257. Height 30.8 mm. V–W. Silicone cast of paratype MGUH 33258. Width of teleoconch 5.5 mm. Width of protoconch 0.7 mm. X. Vexillum tenestolidum n. sp., Silicone cast of holotype MGUH 33259. Width of teleoconch 4.3 mm.