They're sometimes described as a kind of jellyfish, although despite the ... Velellas have two main body parts: an iridescent blue or purple disc and a transparent "sail" disc extending up from ...

Not only is it not a jellyfish, it's not even an "it," but ... Man-of-wars are also known as bluebottles for the purple-blue color of their pneumatophores. The tentacles are the man-of-war's ...