WOW! This is not a jellyfish. It's a COMB JELLY! A siphonophore! One of the very wished animals for be seen in an aquarium for me. But they're very rarely kept in aquariums. You're really very lucky!
Thank you Kakapo and jayjds2 for this additional information, didn't realize that the species was not a common species in captivity when I took the photo !
@jayjds thanks for the info, in my only time in America (San Diego) I have been in two aquariums (SeaWorld and Birch), and none of them have comb jellies. In my own country and not far from my home city, Barcelona Aquarium kept the species Mnemiopsis leidyi, that I guess is the less rarely kept species of the group. However when I visited, the tank that formerly holded them was empty.
