Blue Ring?

[Delphinus]

They're amazing beautiful creatures, and their tiny size is amazing.

I remember seeing one in captivity many years ago at a basement op store. No bigger than a tennis ball.

It's too bad they're extremely dangerous, incredibly clever and adept escape artists (and can squeeze into the most insanely small crevasses), and have such short livespans. This one is best left in the ocean.

Actually I kind of feel that way about any cephalopod, but I suppose there are good examples of dedicated setups out there for them. But it can never be a casual decision to "try" one.