[Proceedings of the symposium 'Molluscan Palaeontology' : 11th International Malacological Congress, Siena (Italy) 30th August - 5th September 1992 / A.W. Janssen and R. Janssen (editors)]: Taxonomy, evolution and spreading of the turrid genus Spirotropis (Gastropoda: Turridae)

The species of the European turrid genus Spirotropis are reviewed and the possible pathways of the evolution and spreading of the genus during the Neogene are outlined. Nine species are recognised: S. spinescens (Bellardi), S. badensis sp. nov. (Middle Miocene, Paratethys), S. karamanensis sp. nov. (Middle Miocene, Turkey), S. tortonica sp. nov. (Late Miocene, Mediterranean Basin), S. gramensis sp. nov. (Late Miocene, North Sea Basin), S. modiolus (de Cristofori & Jan) (Early Pliocene, Mediterranean Basin), S. confusa (Seguenza) (Pliocene to Recent, North Sea Basin to Mediterranean Basin), S. monterosatoi (Locard) (Recent, Morocco to Iberian Basin), and S. azorica Bouchet & Warén (Recent, Azores). The ancestral form is Spirotropis (s.lat.) spinescens (Bellardi) from the Miocene of the Vienna Basin. During the Middle Miocene (Langhian) the genus migrated to the Mediterranean Basin where the species S. karamanensis and S. tortonica evolved. During the Messinian salinity crisis the genus became extinct in the Mediterranean. In the Atlantic domain S. gramensis developed during the Late Miocene in the North Sea Basin. This species was transformed to the Late Pliocene to Recent S. confusa. During the Early Pliocene S. modiolus occurred in the Mediterranean, but probably died out at Mid-Pliocene. S. confusa migrated then from the Atlantic to the Mediterranean during the Late Pliocene. The development of the genus is characterised by the change of the mode of larval development from probably planktotrophic to lecithotrophic which seems to be correlated with progressive cooling of the seawater. The direct larval development became the starting point for a speciation process which led to the formation of several different species in various stratigraphical horizons and geographical regions.