Phylogeny, speciation and species turnover. The case of the Mediterranean gastropods of genus Cyclope Risso, 1826

The genus Cyclope Risso, 1826 (family Nassariidae) has appeared in the foss il record since the Pliocene. Although it is still found today, the teleoco nch morphology has never undergone modification, despite the fact that the protoconch morphologies of fossils (multispiral) and living forms (paucispi ral) are different. They vary in their embryological and larval development and, hence, are two different species: C. migliorinii (Bevilacqua, 1928), the fossil species, and C. neritea (Linnaeus, 1758), the living species. We discuss the morphologic modifications in the evolution of this genus: the speciation that leads to its appearance and the speciation driving the Plio cene species to the living one. The order and the direction of these change s are based on phylogenetic analysis. No intermediate forms have been found showing a gradual morphological change that could have been worked by natu ral selection. Our analysis takes as the origin of the morphological novelt ies the genetic modifications in the ontogenetic processes which resulted i n rapid and important phenotypic changes. Both speciation processes are sym patric cladogenetic. The changes that determine the appearance of the genus affect only the teleoconch, nor the larval development. The modifications that lead from one species to the other, within the genus Cycope, affect th e larval development exclusively. This points to a certain disconnection be tween the development of the embryo-larval phase and the young-adult format ion, such that evolutionary processes could have occurred independently in different ontogenetic stages. The influence of larval ecology in relation t o extinction of the ancestor and persistence of the derived species is also analysed. We hypothesize that climatic fluctuations may have affected the planktonic larvae of the fossil species, driving it to extinction. The livi ng species, developing without the planktonic phase, would have resisted th ese climatic changes. We consider that the mechanisms described as drivers of the evolution of this genus can be of more general validity in prosobran ch gastropods.