Molecular evidence for cryptic species of Aurelia aurita (Cnidaria, Scyphozoa)

Morphological taxonomy suggests that marine faunas are species poor compare d to terrestrial and freshwater faunas (1). This dichotomy has been attribu ted to the unique potential of marine plankters for distant dispersal acros s homogenous oceans with few barriers to gene flow (2). The relative scarci ty of opportunities for allopatric divergence has resulted in depauperate m arine faunas characterized by a high proportion of widespread or cosmopolit an species. Aurelia aurita (Linnaeus) has been considered a good example of such a cosmopolite (3, 4, 5, 6). However, recent molecular studies have re vealed cryptic species in many marine taxa (7). suggesting that marine biod iversity is higher and opportunities for speciation have been more frequent than generally recognized. Here, we present nuclear and mitochondrial DNA sequence evidence of seven sibling species of Aurelia aurita and two additi onal species, A. limbata Brandt and A. labiata Chamisso & Eysenhardt. These sequence data indicate speciation events as early us the late Cretaceous o r early Tertiary, consistent with the formation of well-recognized biogeogr aphic barriers to gene flow in the seas.