I Do Not Wish to Share the Seas

What are these then?

Strange objects drifting round in outer space, perhaps, with a blue moon in the background?

Well, the moon bit's right. The strange, semi-transparent objects are moon jellyfish. The one in the foreground is upside down, and the other one has its circular top facing us, with the underneath facing away.

These particular jellyfish live in a big tank at The Deep in Hull. The blue bit is the top of the tank. The jellyfish are not really blue: they're almost transparent, but live in ultra-violet light so they show up more, and drift round like little blue ghosts.

Flanders and Swann wrote, about much bigger jellyfish, the Portuguese Man O'War:

I do not wish to share the seas/ With jellyfishes such as these/Particularly Portuguese.

I found the moon jellyfish fascinating and strangely hypnotic to watch, but I still don't think I'd like to swim with them.