Hasselbachia Korn & Weyer, 2003

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 161

Genus Hasselbachia Korn & Weyer, 2003

Type species

Imitoceras multisulcatum Vöhringer, 1960: 141 ; original designation.

Genus diagnosis

Genus of the Gattendorfiinae with a discoidal to pachyconic conch with low coiling rate (WER = 1.50– 1.70); inner whorls subevolute or evolute, umbilicus in the adult stage not completely closed. Ornament usually with coarse, convex or slightly biconvex growth lines. Suture line with deep, V-shaped external lobe (as deep as adventive lobe).

Genus composition

Central Europe ( Vöhringer 1960): Imitoceras multisulcatum Vöhringer, 1960 ; Imitoceras gracile Vöhringer, 1960 ; Hasselbachia erronea sp. nov.

North Africa ( Ebbighausen et al. 2004; Ebbighausen & Bockwinkel 2007): Hasselbachia gourara Ebbighausen, Bockwinkel, Korn & Weyer, 2004 ; Hasselbachia arca Ebbighausen & Bockwinkel, 2007 .

Remarks

Several characters allow a clear separation from the superficially similar species of other genera, such as Paragattendorfia and Stockumites . The low aperture and hence slowly expanding whorls (WER ~ 1.50 in the adult stage) is in contrast to Stockumites , in which this value usually ranges between 1.70 and 1.90. Species of Paragattendorfia have similarly low coiling rates (WER ~1.45), but in Hasselbachia , the umbilicus is wide only in the inner whorls, followed by an incomplete adult closure by a significant overlap of the flanks upon the umbilicus. In Paragattendorfia , the uw/dm ratio is rather constant throughout ontogeny. Hasselbachia is remarkable because it combines characters, which are present in other genera: the low WER as in Mimimitoceras , the continuous opening of the umbilicus in the inner whorls as in Paragattendorfia and closure of the umbilicus is more similar to Stockumites .

Kullmann (2009) regarded Hasselbachia as probable synonym of the subgenus Acutimitoceras (Stockumites) , but the clear distinguishable characters (e.g., the very low coiling rate in Hasselbachia ) make such a decision obsolete. Apart from the coiling rate, the different shape of the inner whorls justify the independence of the genus and can be used as an indication for a phylogenetic placement of Hasselbachia in an evolutionary lineage within the subfamily Gattendorfiinae .