The systematic position of the fossil species referred toCalliotropisis currently under debate due to the striking resemblance between these forms with their extant counterparts in general shell morphology and ornament pattern. We propose two temporal subgenera ofCalliotropis:Calliotropis(Riselloidea) for Mesozoic species andCalliotropis(Calliotropis) for Cenozoic and Recent taxa. We also synonymize the families Eucyclidae and Calliotropidae, and redescribe the type genus of Eucylidae based on topotypic material ofE. obeliscusfrom Normandy. We argue that the generic nameAmberleyashould be restricted to its type speciesAmberleya bathonica. For the species that were traditionally included inAmberleya, we propose the new genusAmbercyclus, with its type speciesAmberleya orbignyana. The present paper also provides descriptions of threeCalliotropisspecies from the Early Jurassic marine deposits of Argentina. The occurrence ofCalliotropis(Riselloidea)keidelin. sp.,Calliotropis(Riselloidea) cf.C. (R.)keideliandCalliotropis(Riselloidea) sp. in the Jurassic of Chubut and Neuquén provinces represents a new record of the genus in Early Jurassic sediments of Argentina and South America. Moreover, two species ofAmbercyclusn. gen., such asAmbercyclus espinosusandAmbercyclus?isabelensisn. sp., are described from the same deposits.Eucyclus,Amberleya,Ambercyclus, andCalliotropisare included into Eucyclidae, which we consider to be a family of Seguenzioidea.

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Abstract.-Early Jurassic marine gastropods are well represented in Argentina by three major taxa: Vetigastropoda, Caenogastropoda and Architectibranchia ( = Opisthobranchia). The present paper aims at the description of six new caenogastropod species and one new architectibranch species from the Early Jurassic marine deposits of the Neuquén

Based on an exhaustive database of gastropod genera and subgenera during the Triassic–Jurassic transition, origination and extinction percentages and resulting diversity changes are calculated, with a particular focus on the end-Triassic mass extinction event. We show that gastropods suffered a loss of 56% of genera and subgenera during this event, which was higher than the average of marine life (46.8%). Among molluscs, gastropods were more strongly affected than bivalves (43.4%) but less than ammonoids, which were nearly annihilated. However, there were also pronounced differences among gastropod subclasses. The most strongly affected subclass was the Neritimorphia, which lost 72.7% of their Rhaetian genera; on the other extreme, the Heterobranchia remained nearly unaffected (11% loss). We analysed this extinction pattern with respect to larval development, palaeobiogeography, shell size, and anatomy and found that putative feeding of the pelagic larval stage, adaptation to tropical-temperate water temperatures, and flexibility of the mantle attachment were among the factors that might explain extinction resilience of heterobranchs during the end-Triassic crisis. Among molluscs, extinction magnitude roughly correlates with locomotion activity and thus metabolic rates. We suggest three potential kill mechanisms that could account for these observations: global warming, ocean acidification, and extinction of marine plankton. The end-Triassic extinction of gastropods therefore fits to proposed extinction scenarios for this event, which invoke the magmatic activity of the Central Atlantic Magmatic Province as the ultimate cause of death. With respect to gastropods, the effect of the end-Triassic mass extinction was comparable to that of the end-Permian mass extinction. Notably, Heterobranchia was relatively little affected by both events; the extinction resilience of this subclass during times of global environmental changes was therefore possibly a key aspect of their subsequent evolutionary success.