Does anyone know this jellyfish by name?

A reader from the UK sent me these lovely photos that he took of a jellyfish and asked for my help in identifying it. Unfortunately, while I'm pretty good with bacteria, plants, and tropical fish, my taxonomy skills don't go much farther unless I have a sample of DNA. These photos were taken at La-Manga off the coast of southern Spain. My Sciblings have guessed: Rhizostoma, Stomolophus meleagris, or Mastigas If you know, we'd all appreciate an answer in the comments. And if you don't know about much jellyfish, RPM at evolgen would like your help answering a different reader's question: When a manatee swims, does it get water up its up nose?