Tectus indecorus, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 75-76

Tectus ? indecorus n. sp.

Figs 22 L–N

2014 Tectus sp. Hansen & Surlyk: tab. 3.

Diagnosis. High-spired with weakly convex whorls. Columella nearly straight, oriented slightly oblique to axial line; columellar fold nearly effaced. Transverse ribs short and strong, numbering around 10 per whorl. Spirals finely tuberculated, present on base as well as spire whorls.

Derivation of name. Refers to the generally worn and rather ugly appearance of the specimens at hand.

Type material. Holotype MGUH 33116 is an external mould with protoconch . Paratype ØSM.10042-327-a and b is an external and internal mould of the lower teleoconch whorls from the same stratigraphic level north of Kulsti Rende , Stevns Klint .

Additional material. Two weathered moulds ( ØSM.10042-182-a–b, ØSM.10042-253-a–b).

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

Occurrence. Lithified top of the Maastrichtian Højerup Member at Stevns Klint.

Description. Protoconch obtusely conical to dome-shaped paucispiral with close to two smooth whorls separated by shallow suture. Protoconch width approximating 0.6 mm.

Teleoconch trochiform with weakly convex whorls and shallow suture. Whorl height corresponding to nearly half the width of early whorls, decreasing to one third on later whorls. Base flattened with no umbilicus. Aperture subrectangular with short and weakly convex columellar lip, oriented slightly oblique to axial line. Columellar fold nearly completely effaced.

Teleoconch sculpture dominated by around 10 strong, bulbous transverse ribs per whorl on abapical whorl half. Spire whorls additionally covered by fairly coarse and irregular spiral threads, which are heavily tuberculated due to cancellation by slightly sigmoid and strongly prosocline growth lines. Base finely tuberculated due to interference between strongly prosocline and opisthocyrt growth lines and finer, more densely spaced spiral threads.

Measurements. Holotype MGUH 33116 is 2.0 mm high and 1.6 mm wide, consisting of protoconch and about 3 ½ teleoconch whorls. Paratype ØSM.10042-327-a has a width of at least 20.3 mm.

Remarks. Tectus ? indecorus n. sp. to some degree resembles the Campanian Tectus sensuyi ( Vidal, 1921) from Torallola in Spain, but is easily distinguished by the fewer transverse ribs and the presence of spiral sculpture on the base. Of the two species encountered in the early Danian limestone of Belgium it is most similar to Tectus carinadentatus ( Briart & Cornet, 1887) , but differs by the absence of a strong columellar fold, the higher spire and by the coarser and sparser transverse sculpture. The relatively high whorls and that the transverse whorls appear better developed on the adapical whorl surface than at the keel may suggest that the species do not belong in this genus, though a few recent species do feature somewhat similar characteristics.

Figures

FIGURE 22. A. Phorcus sp., Silicone cast of MGUH 33109. Exposed width 2.2 mm. B–C. Stomatella sp., External mould of MGUH 33110. Figure B has been colour inverted and mirrored to show it in positive. Width 1.5 mm. D–F. Solariella sp. D–E. Silicone cast of MGUH 33111. Width 6.2 mm. F. Silicone cast of aperture of MGUH 33112. Width 5.95 mm. G–I. Skenea sp. G–H. Inner mould of MGUH 33113. Width 5.2 mm. I. Inner mould of MGUH 33114. Width 10.2 mm. J–K. Leucorhynchia sp., Silicone cast of MGUH 33115. Width 2.4 mm. L–N. Tectus? indecorus n. sp., L. Umbilical view of inner mould of paratype ØSM.10042-327-b. Width 19.7 mm. M–N. Silicone cast of holotype MGUH 33116. Width 1.7 mm. O–P. Homalopoma sp., Silicone cast and inner mould of MGUH 33117. Width 9.6, 6.9 mm respectively. Q. Calliomphalus (Calliomphalus) sp., Silicone cast of MGUH 33118. Width 3.1 mm. R–U. Arene jakobseni n. sp. R–T. Silicone cast of holotype MGUH 33119. Width 8.6 mm. U. Silicone cast of paratype MGUH 33120. Width of aperture 4.8 mm.