Riselloidea Cossmann, 1909

Szabó, János, 2018, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 4. New eucycloidean, trochoidean, neritimorph, and caenogastropod taxa in the fauna of the Hierlatz Alpe (Hallstatt, Austria), Fragmenta Palaeontologica Hungarica 35, pp. 61-84 : 64

Genus Riselloidea Cossmann, 1909

Type species – Risellopsis subdisjuncta Cossmann, 1908

Remarks – FERRARI et al. (2014) and FERRARI & KAIM (2018) discussed the relations between the fossil and recent eucycloideans and concluded that the shell morphology of Calliotropis and Riselloidea does not differ significantly because “the absence/presence of umbilicus seems to be an unstable character”. This is true for the cases when anomphalous and umbilicate species equally occur with similar shells more or less contemporaneously, e.g. in most pleurotomariid genera. If the two species groups are so clearly separated temporarily like in the case of Riselloidea (Mesozoic) and Calliotropis (Cenozoic to Recent), both the lack and presence of an umbilicus must be accepted as genus characters. Additional data, like shape and size differences in the protoconchs of the two groups ( FERRARI et al. 2014, p. 1181), emphasize the distinction of these genera.

FERRARI & KAIM (2018) mention two umbilicate Jurassic species which might support the unification of the two genera. From these species, Riselloidea multistriata (Böckh, 1874) has only a pseudoumbilicus; actually it is anomphalous, while the periaxial basal region in Calliotropis erraticus Gründel & Kopka, 2007 (Pl. 1, Fig. 3) remained filled by sediment in its monotype. Inference of an umbilicus, reflected in the diagnosis of this species needs yet verification. The early teleoconch morphology of Riselloidea indicates its family position in Eucycloscalidae Gründel, 2007 .