Last week my friend Jeff sent me a link to a really fascinating article about  Turritopsis dohrnii – the “immortal” jellyfish. Turns out this little animal never seems to die but rather it sort of morphs backwards when it reaches the last stage of its reproductive cycle. For most jellyfish, their life cycle alternates between two stages – the polyp stage, which is rooted to the substrate and can reproduce asexually, and the medusa stage, which is the more familiar “swimming” jelly stage and reproduces sexually. What the immortal jelly does different is, after reproducing as a medusa, the animal first turns back into an amorphous blob of undifferentiated cells before shooting up stalks that turn into new polyps. Never before has this reversal been noted in another species – polyps turn into medusae but not the other way around! Until now, of course. It remains unclear as to what, exactly, this news means to us humans. Dr. Shin Kubota,a researcher in Japan, has been growing T. dohrnii in his lab for the past few years. He, for one, is convinced that the secrets of the immortal jellyfish can be applied to us humans so that one day we too could be immortal. I am not so sure about this, seeing as how the “regeneration” event from medusa to polyp stage involves a complete reorganization of the body plan (imagine, in order to keep on living, your body has to revert to an infant!). Nor is it clear that immortality would be a great thing for all 7 billion (and counting) of us humans already here on earth. Nevertheless, it is a fascinating story about a fascinating species, one that belongs to a group of creatures called the Cnidarians.

Upside-down jelly

Another amazing Cnidarian is the upside-down, or Cassiopeia jelly. These guys live all over the canals and shallow backwaters of the Florida Keys. Like corals, they have photosynthetic zooxanthellae that provide the jellyfish with energy and their greenish coloration. The symbiotic algae hitches a ride with the jellyfish, trading the protection afforded by a nest of stinging tentacles for extra food that it provides to the jellyfish. All in all, two amazing examples of Phylum Cnidaria.