I personally prefer the pet version called little sail (Velella velella). Supercute floating city and harmless to touch (I had put them in my hands). Its predator, the blue sea dragon definitely can sting. It eats blue bottles and store the poison cells as weapon, so if you don't look out, you could get more than you expect.

Those blue dragons and the deep sea Siphonophores (with cool floaters shaped like cut crystal spaceships) are among the most alien things in this planet. I don't even want to imagine how much more poisonous than blue bottles could be those deep sea species in its habitat.

I bet that NASA researchers salivate about the idea of how much similar things could live in Europe's ocean waiting to be discovered.