Eucycloidea bitneri, Nakrem, 2017

Nakrem, Hans Arne, 2017, Gastropods from the Late Jurassic - Early Cretaceous seep deposits in Spitsbergen, Svalbard, Zootaxa 4329 (4), pp. 351-374 : 356-357

Eucycloidea bitneri sp. nov.

( Fig. 4 )

2011 Eucyclus sp.; Hammer et al. 2011, fig. 7l,

2015 Ambercyclus sp.; Hryniewicz et al. 2015a, table 1.

Diagnosis. Shell trochiform, with strong, nodose medial keel, nodes merge later into band. Flank ornamented by dense network of tiny axial and spiral riblets. Base with strong spiral ribs.

Holotype: PMO 217.235, H = 46 mm, W = 33 mm.

Type locality and age: Seep #3, Sassenfjorden, Svalbard; late Tithonian, Late Jurassic.

Other material: Fourteen specimens from seep #3, three specimens from seep #9, and two specimens from seep #13 ( Table 1).

Description. Protoconch unknown. Shell trochiform with strong medial keel. Additional keels are present just at the adapical and abapical suture. The lateral flank is covered by numerous fine axial riblets. Above the medial keel, the riblets are strongly opisthocyrt while below the medial keel only weakly opisthocyrt. The medial keel is covered by a series of blunt, smooth and wide nodes, the other keels are intersected by axial riblets though later in ontogeny these ribs become similar to the medial keel and the nodes on medial keel tend to merge into single band. The intersection of axial riblets and abapical keel is strongly inclined prosoclinally. The inter-keel surfaces are concave and ornamented by tiny spiral grooves (striae). The base is ornamented by 4–6 strong spiral ribs and tiny prosocline axial riblets. Growth lines strongly prosocline. Aperture, umbilicus, inner and outer lip not preserved.

Remarks. Eucycloidea bitneri differs from other species in the genus by having an exceptionally strong spiral keel with nodes merging into a band. It also possesses delicate reticulate ornament on the lateral flank. The type species, E. bianor (d’Orbigny, 1850) differs by possessing additional tiny nodes on the intersection of axial and spiral riblets ( Gründel 1997, 2003). E. tenuistria (Münster, 1844) (in Goldfuss 1844) from the Aalenian (Middle Jurassic) of Germany has weaker and less rounded nodes on the keel ( Schulbert & Nützel 2013). The Middle Jurassic E. granulata ( Hébert & Eudes-Deslongschamps, 1860) from France differs by possessing spiral riblets also on the keel ( Gründel 2000). The Middle Jurassic E. badamuensis Ferrari et al., 2016 from Iran ( Ferrari et al. 2016) differs by having more pronounced spiral cords rather than tiny riblets, and regularly spaced and clearly separated nodes on the keel throughout ontogeny. The juvenile specimens ( Fig. 4D , PMO 224.753) from late Berriasian seep # 9 may represent another species, as they have smaller and more numerous spiral ribs on the base ( Fig. 4D ) than the specimens from the Tithonian localities.

Distribution. Seep #3 (late Tithonian); seep #9 (late Berriasian), and seep #13 (late Tithonian); Sassenfjorden, Svalbard.

Etymology. In honour of Maria Aleksandra Bitner, a specialist of fossil and modern brachiopods.

Figures

FIGURE 4. Eucycloidea bitneri sp. nov. Sassenfjorden, Svalbard. A – C. Holotype (PMO 217.235), Seep deposit # 3; late Tithonian (Late Jurassic). D. Juvenile (PMO 224.753), Seep deposit # 9; late Berriasian (Early Cretaceous).