These "jelly fish" are both beautiful and terrifying. Siphonophores Colonial Organism or Complex Organism
While they were thought of as jelly fish for some time, their exact classification has been under serious scrutiny lately. Due to their deep ocean living situation, studying their lifecycle has proven difficult, making it really hard to asses exactly what they are.
Portuguese Man-O-War are named so not because they come from Portugal, but rather because they look like the Man-O-War tall ship that the Portuguese used back in the age of sail. The creature has tentacles like a jellyfish, but instead of a bell filled with fluids it has a balloon. Instead of undulating the bell for locomotion, it raises a sail to the wind.
As if these creatures weren't interesting enough, their very classification as an organism has come into question. Portuguese Man-O-War are Siphonophores, but that is kind of the best we can do when it comes to classifying them. It turns out that the creature is more akin to a colony than a single organism. Each major part of the Man-O-War seems to be its own creature, capable of living on their own without the direct need of the other organisms. At the same time, each organism that makes up the "colony" is so highly specialized that it resembles tissues in different organs, making this a complex organism instead of a colony.
Sadly, this creature is so confusing and interesting that scientists still don't fully know how to classify it. Should it be a colony made up of obligate mutualistic organisms or is it actually a complex organism made up of various organs, and not various organisms? It seems like a simple question to ask and answer, but the various parts of the Man-O-War exhibit both traits and therefore it continues to perplex scientists.