What do you get when you combine the immortality of Highlander with the backwards aging ability of Benjamin Button? Turritopsis dohrnii, the immortal jellyfish! This little invertebrate is smaller than a pinky nail, measuring about 4.5mm wide in its adult state, but credited with being able to live forever. Of course, this excludes extreme physical damage or being eaten.
The highlander of the sea is what's called a hydrozoa, a class of invertebrates that can live in freshwater or the ocean, and immortal jellyfish can be found all over the world. They are transparent with a bright red stomach and can have up to 90 tentacles. Turritopsis dohrnii can also easily be confused with Turritopsis nutricula and rubra, which look similar but don't come with the cool immortality feature.
While there are still many mysteries regarding immortal jellyfish, these tiny creatures are important to humanity for obvious reasons. But is this jellyfish really immortal? And, more importantly, would Connor MacLeod approve?