Hasselbachia erronea Korn & Weyer 2023, sp. nov.

Hasselbachia erronea sp. nov.

urn:lsid:zoobank.org:act: D15B0445-7E34-47E3-9A31-E00C5E5B70C8

Figs 101–102; Tables 98–99

Acutimitoceras sphaeroidale – Vöhringer 1960: 143, text-fig. 21. — Korn 1992b: 17, pl. 2 figs 30–31. — Schönlaub et al. 1992: pl. 5 figs 30–31. — Korn 1994: text-figs 50f, 51b.

Diagnosis

Species of Hasselbachia with a thickly pachyconic and involute conch at 15 mm dm (ww/dm ~0.75; uw/dm ~0.10); whorl cross section moderately depressed (ww/wh ~1.65); coiling rate very low (WER ~1.60). Flanks moderately strongly converging. Fine lamellar growth lines with convex course. Shell and internal mould with constrictions extending across the venter.

Etymology

From the Latin ‘ erronea ’, referring to the previous misunderstanding of the material.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; illustrated in Fig. 101; MB.C.31198.

Paratypes

GERMANY • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 5; Vöhringer Coll.; GPIT-PV-63932, GPIT-PV-63927 • 1 specimen; Rhenish Mountains, Oese, old quarry; bed interval III; Paproth Coll.; MB.C.5286 • 1 specimen; Rhenish Mountains, Oese, old quarry; bed interval IV; Paproth Coll.; MB.C.5283.1.

Description

Holotype MB.C.31198 (Fig. 101) has 16 mm conch diameter and is thickly pachyconic with a very narrow umbilicus (ww/dm = 0.75; uw/dm = 0.09). The specimen possesses broadly rounded flanks that merge with a continuous curve into the evenly rounded venter. The umbilical margin is rather narrow. The shell bears an ornament with fine, widely spaced growth lines, which extend almost straight across flanks and venter, forming only a low lateral projection (Fig. 102B). Parallel to the growth lines extend very faint shell constrictions, spaced about 120 degrees apart.

The sectioned paratype GPIT-PV-63927 allows the study of conch ontogeny up to a diameter of 15 mm (Fig. 102A). It shows the transition from the juvenile stage with a kidney-shaped whorl profile to a C-shaped whorl profile at about 7 mm conch diameter. It can be observed that the absolute width of the umbilicus does not change above about 7 mm conch diameter. Accordingly, the uw/dm ratio is reduced from ~0.30 to ~0.15 between 7 and 15 mm conch diameter. The suture line of the specimen has a lanceolate, narrow external lobe with weakly convergent flanks. It is followed on the flank by a rather narrow, tightly rounded ventrolateral saddle and a narrow, V-shaped adventive lobe (Fig. 102C).

Remarks

Hasselbachia erronea sp. nov. is described here as a new species on the basis of the paratypes of “ Imitoceras sphaeroidale Vöhringer, 1960 ”. These three paratypes clearly differ from the holotype of that species in their much more slender conch and the presence of shell constrictions and cannot be included in the same genus.

Hasselbachia erronea sp. nov. differs from the species H. gracilis and H. multisulcata by the constrictions that extend across the venter in the new species.