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

Morphological taxonomy suggests that marine faunas are species poor compared to terrestrial and freshwater faunas (1). This dichotomy has been attributed to the unique potential of marine plankters for distant dispersal across homogenous oceans with few barriers to gene flow (2). The relative scarcity of opportunities for allopatric divergence has resulted in depauperate marine faunas characterized by a high proportion of widespread or cosmopolitan species. Aurelia aurita (Linnaeus) has been considered a good example of such a cosmopolite (3, 4, 5, 6). However, recent molecular studies have revealed cryptic species in many marine taxa (7). suggesting that marine biodiversity 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 additional species, A. limbata Brandt and A. labiata Chamisso & Eysenhardt. These sequence data indicate speciation events as early us the late Cretaceous or early Tertiary, consistent with the formation of well-recognized biogeographic barriers to gene flow in the seas.