MIGLIETTA , M.P.; SCHUCHERT , P.; Duke University; Mus�um d’histoire naturelle, Gen�ve , Switzerland: The Phylogeny of the genus Turritopsis (Hydrozoa – Cnidaria)-The immortal jellyfish

The ability to revert its life cycle, thus becoming potentially immortal, brought some unexpected fame to the otherwise inconspicuous jellyfish genus Turritopsis. The process of transdifferentiation enables the jellyfish to avoid death by returning to a juvenile stage after it has spawned or if it suffers from adverse environmental conditions. Although the genus is quite well known and distinct, it is presently unclear how many biological species it encompasses. The influential synopsis of Kramp (1961) considered only two species worldwide. Most populations were attributed to Turritopsis nutricula, which was regarded to be a cosmopolitan species. Small differences in the various geographic populations have been noted by some authors, but set aside as intraspecific variation. Intriguingly enough, only some populations of the reportedly cosmopolitan Turritopsis nutricula are able to transdifferentiate (one in the Mediterranean Sea and the other one in Japan). This hinted at the possibility that Turritopsis nutricula might actually be a species complex. Careful comparisons of their reproductive strategies and the morphology of living animals showed that several distinct morphotypes, and thus putative biological species, can be distinguished. Our investigation using molecular techniques (using mitochondrial 16S and ribosomal 18S sequences) confirmed that some of the different morphotypes indeed correspond to distinct phylogenetic lineages, thus likely different species. The molecular results also suggest that the Mediterranean form of Turritopsis, the one that is able to transdifferentiate, has recently been introduced to Japan. Some of the Japanese and Mediterranean animals have identical sequences. This suggests that the ability to transdifferentiate might also favor its ability to be transported by human activities.