The biogeography of the tropical western Atlantic is of great interest and fascinating complexity. The Pliocene closure of the isthmus of Panama about 3 Mya that separated the Atlantic and the Eastern Pacific oceans, the network of Caribbean islands of different ages, coupled with Pleistocene transient allopatry caused by sea-level changes generated a unique setting for recent biological diversification and extinction. But the impact of all these processes in shaping the origin of the marine biodiversity of the region is still poorly understood. In this project the bubble-shell Bulla occidentalis is used as a model-species to shed light on the mechanisms of marine diversification in the Caribbean. A combination of molecular phylogenetics, population genetics, and historical biogeographic reconstruction is used.