Vexillum tenestolidum, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 139

Vexillum tenestolidum n. sp.

Figs 30X , 31 A–C

Diagnosis. Protoconch obtusely conical with around two and a half moderately inflated whorls. Teleoconch small, slender with around 12 to 14 distinct transverse ribs per whorl on adapical five whorls, changing to fine but unevenly cancellate sculpture on later whorls.

Derivation of name. Compound word for obtuse (stolidus) and young (tener), referring to the obtusely conical protoconch.

Type material. Holotype MGUH 33259 is a nearly complete mould with protoconch collected by A. Rosenkrantz in 1943 . Paratype MGUH 33260 is an external mould collected by K.I. Ingemann in 1986 from Dania Quarry, Northern Jutland .

Additional material. Two moulds with informal sample numbers SH.278 and SR.376, and 33 uncatalogued and more or less fragmentary moulds are found in the collections of the Natural History Museum of Denmark.

Type stratum and type locality. The lower Danian Cerithium Limestone Member at Skeldervig, Stevns Klint .

Occurrence. Relatively common in the Cerithium Limestone Member at Stevns Klint and the corresponding ‘dead layer’ at Dania, Northern Jutland.

Description. Protoconch obtusely conical with around 2 ½ low, inflated whorls, possible smooth. Transition to teleoconch sharp, marked by distinct change in spire angle and the appearance of transverse ribs.

Teleoconch slender, fusiform with high, flattened whorls, which are only around 1.5 times as wide as high. Whorls separated by marked suture. Whorls widest centrally or slightly adapically from here and characterized by distinct constriction slightly abapically of adapical suture. Last whorl takes up approximately 2/3 the total shell height, while aperture corresponds to around 40 %. Aperture narrow with weakly convex outer margin and sigmoid inner margin; columella carrying four strong folds, their distance and strength decreasing abapically from parietal region to wide siphonal canal.

Teleoconch sculpture on first five whorls dominated by around 12 to 14 moderately sharp and strong transverse ribs per whorl, which due to adapical constriction appear strongest just over 1/3 the whorl height from adapical suture, forming a slight shoulder on the whorl. Transverse ribs cancellated by relatively weak and densely spaced spiral threads. Transverse ribs becoming finer and closely spaced on later whorls; in some specimens even replaced by distinct growth lines of a like strength with the spiral threads.

Measurements. Holotype MGUH 33259 is 14 mm high and 4.8 mm wide, consisting of six teleoconch whorls. Protoconch measuring 0.7 mm in width and 0.5 mm down to teleoconch suture.

Remarks. The Danish taxon corresponds well to the subgenus Vexillum Röding, 1798 except in the multispiral protoconch, which differs from the typical form by its obtusely conical shape.

According to Stilwell (2003) the oldest members of the subgenus Vexillum appears around the Cretaceous-Palaeogene boundary, and the Danish taxon could therefore perhaps represent an early form or merely a close relative.

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.

FIGURE 31. A–C. Vexillum tenestolidum n. sp. A–B. Silicone cast of holotype MGUH 33259. Width of protoconch 0.7 mm. Width of last whorl 3.4 mm. C. Silicone cast of paratype MGUH 33260. Width 5.8 mm. D–G. Vexillum? rosenkrantzi n. sp. D–E. Silicone cast and inner mould of holotype MGUH 33261. Width 1.9 and 1.6 mm respectively. F. Silicone cast of paratype MGUH 33262. Width 3.2 mm. G. Silicone cast of paratype MGUH 33263. Width 2.9 mm. H. Vexillum? sp. Silicone cast of MGUH 33264. Width 3.5 mm. I. Columbarium heberti (Briart & Cornet, 1880). Silicone cast of last whorl MGUH 33265. Width 7.7 mm. Photograph by S.L. Jakobsen. J. Columbarium sp. Silicone cast of MGUH 33266. Width 13.3 mm. K–N. Conomitra glabra (Ravn, 1902). K. Silicone cast of MGUH 33267. Width 3.6 mm. L–M. Silicone cast of MGUH 33268. Width 3.6 and 3.9 mm respectively. N. External cast of syntype MGUH 116. Height 8.2 mm. Photograph by S.L. Jakobsen. O. Volutomitra cf. quinqueplicata Ravn, 1902. Silicone cast of MGUH 33269. Width 11.6 mm. P. Volutomitra quinqueplicata Ravn, 1902. External cast representing last whorl of type specimen MGUH 117. Middle Danien Faxe Formation, Denmark. Height 38.6 mm. Photograph by S.L. Jakobsen. Q–R. Spirancilla milthersii (Ravn, 1902). Q. Silicone cast of holotype MGUH 33270. Width 3.3 mm. R. Silicone cast of MGUH 33271. Width 3.1 mm. S–T. Exilia sp., Silicone cast of MGUH 33272. Width 1.6 mm. U–W. Latiromitra? sp. External cast and inner mould of MGUH 33273. Width 4.6 mm for casts and 4.0 mm for mould.