Boreoscala similis (J. de C. Sowerby, 1813)

Boreoscala similis (J. de C. Sowerby, 1813) View in CoL ( Fig. 7A View FIG 1-A View FIG 3 View FIG , B 1-B View FIG 3 View FIG )

Scalaria similis J. de C. Sowerby, 1813: 49 , pl. 16, two upper figures.

non Scalaria similis G.B. Sowerby II, 1844: 94 , pl. 34, fig. 90 [synyonym of Epitonium jomardi (Audouin, 1826) View in CoL ] (non J. de C. Sowerby, 1813).

Scalaria groenlandica – Wood 1848 (partim): 90, pl. 8, fig. 11 (fossil specimens only)[non Boreoscala greenlandica (Perry, 1811]).

Scala (Boreoscala) similis – Harmer 1925: 549, pl. 47, figs 18-22.

Epitonium similis View in CoL – Wesselingh et al. 2012: 174, fig. 18.

MATERIAL AND DIMENSIONS. — Maximum height 35.4 mm, width 13.7 mm. — RGM.1364910 (24), leg. WG ; RGM.1365181 (1), leg. WG ; RGM.1364911 (1), leg. WG ; RGM.1364979 (34), ACJ .

SPECIES CHARACTERISATION. — Robust epitoniid with variable convex to subconvex whorl profile and a characteristic spiral ornamentation of low broad ribs. The whorl profile, number and strength of the ribs, including a basal rib, are very variable.

DISTRIBUTION. — Lower Pliocene: NSB, Coralline Crag Formation, England (Harmer 1925). — Upper Pliocene: NSB, Red Crag Formation, England ( Wood 1848; Harmer 1925), Netherlands ( Wesselingh et al. 2012). — Lower Pleistocene: NSB, England (Harmer 1925); Atlantic, Selsoif, NW France (this paper).

REMARKS

Boreoscala similis (J. de C. Sowerby, 1813) from Late Pliocene warm temperate and temperate assemblages of the North Sea Basin is closely similar to B. greenlandica (Perry, 1811) , an arctic to subarctic-boreal, almost circumpolar species, living today. It differs in having a somewhat thicker shell, with stronger ribs and a more convex whorl profile then B. greenlandica . Extant specimens of the latter are very variable but have generally thinner axial ribs and less impressed sutures, resulting in less convex whorls. The material from Selsoif is closer to B. similis , with a few specimens having less convex whorls and approximating to B. greenlandica . These differences are clearly illustrated by Wesselingh et al. (2012: compare fig. 17 vs fig. 18).

It is tempting to suggest that B. greenlandica evolved from B. similis as a colder water adapted species. However, this is unlikely, as the specimen illustrated as B. greenlandica by Símonarson et al. (2021: pl. 7.8, fig. 6) from the Late Pliocene-Early Pleistocene of Iceland is clearly that species with its shallow suture and weakly convex whorls. Durham & MacNeil (1967) suggested that B. greenlandica was most probably of Pacific origin.

It is also possible that the two represent extreme forms of a single species, and that the differences seen are ecophenotypic. Despite the variability seen in both species, Pliocene specimens in the RGM collections could relatively easily be ascribed to B. similis , and extant specimens to B. greenlandica . In view of this, we maintain the two species separate, and consider the Selsoif material to belong to B. similis .