Fun fact: they’re a type of tunicate, which is in the chordata phylum. This means that they are more related to humans than they are jellyfish and other assorted translucent sea creatures.
Still, jellyfish are fascinating creatures. I was on vacation in Italy this spring (One -very- long day’s drive from where I live) and the beach there was littered with millions of little Vellela jellyfish. Vellela’s or “by the wind sailors” are beautiful, delicate little creatures, like something out of a fairy tale. The have a cornflower blue tiny body, the shape and size of a flower, and a little glass-like transparent tri-angular sail that sticks out above the water and acts as a little sail, transporting the Vellelas across the oceans.
We had a inflatable boat and went behind the surf to see the vellela still alive, still in their element. Every seventh wave was crested with a little sail catching the sun. I looked it up and it turns out this massive crashing of vellella occurred maybe once every twenty years.