(sorry, no pictures today as the only one I could find is restricted for scientific use only.)
Immortality seems to be a high human hope but for the immortal jellyfish, aka turritopsis nutricula, it’s just a day ending with a y. It is very small, only 4 or 5 millimeters in diameter (0.18 inches). Its stomach is bright red and adult nutricula can have as much as 90 tentacles.
The most interesting thing about the Immortal Jellyfish of course is the origin of its name. After one of these little guys reaches sexual maturity it can revert back to a polyp if it gets injured or starts to starve. So essentially it can revert back to childhood if need be and clone itself endlessly, becoming biologically immortal. It is the only known species capable of reverting back to sexual immaturity after having reached maturity. In practice it’s not actually immortal since they cannot revert back to a polyp while they are maturing and often die or get eaten during this period of their lives.