The rock star mantra of "live fast, die young" works in reverse too - you can trade off enjoyment for endurance. Don't smoke, drink or eat meat and you can extend your life by decades, though what you're going to do with all that time is another question. Now it seems that an animal has taken this to the logical extreme, and can live forever - the only drawback being it lives forever as a small clump of jelly.
The Hydrozoan, a small predatory sea creature like a jellyfish but without all their well known exciting higher functions, can achieve the dream of millions and become a child again. When adverse environmental conditions threaten death it can collapse into a rugged blob of cells to survive. When it re-emerges, it does so as a child - literally building itself up all over again. Since this isn't just a shell to hide in, but a complete structural restart, it seems possible that it could keep this up forever.
Since one of these adverse environmental conditions is "getting sucked into the ballast tanks of a freighter", the hardy hitchhiker has spread all over the globe.
It possesses stingers and eats things, which are definitely qualities you don't want in something that's unkillable and spreading worldwide, but if you're larger than a shrimp you're still safe. If you are currently smaller than a shrimp, get Rick Moranis to block the laser and try to be in a better comedy next time.
We aren't in any immediate danger of knock-on effects either, as the jetsetting jellyfish-ettes seem to be integrating quite harmlessly into their new homes (though some shrimp might disagree). The rather damp phoenix-stylings of the hydrozoan have obviously made them a hot topic in genetics, but don't expect to buy your immortality pills just yet - this is one life extension option that isn't even remotely applicable to humans.