Which is a simple freshwater species that is just 15 millimeters in length. Hydras could theoretically live forever one biologists observed the Hydra in a laboratory environment for four years and at the end of the period the Hydra had not aged at all since this experiment it has been concluded by the scientific community that the Hydra is biologically immortal how this works is that hydras have unique stem cells that almost regenerate and live for rest of time.
2. Planarian Flatworm
They are extremely common and can be found in a river. Planarian flatworms have many extraordinary abilities such as the ability to regenerate lost body parts and also total biological immortality. If you slice a planarian flatworm the middle both equal halves would regrow and you would find two identical planarian flatworms that are effectively clones of each other it doesn’t even matter if you cut a planarian at the head or into many times each part it will always regrow a full body. So, it has been described as immortal.
Lobsters have an enzyme that is unique to their anatomy and can repair a repetitive DNA sequences in their genome which allowing cell division to occur with fewer risks research suggests that lobsters do not slow down weaken or even lose fertility with age, in fact, older lobsters are even more fertile than younger lobsters but this is also their greatest weakness as a lobster ages and becomes larger so does the shell it requires the larger the shell a lobster has the more difficult it is to shed the main cause of mortality and lobsters is actually die from exhaustion.
4. Turritopsis dohrnii
The turritopsis dohrnii is truly an immortal creature unlike other species of jellyfish found worldwide in temperate to tropic waters. Turritopsis dohrnii when exposed to environmental stress or physical assault or a sick or old transform themselves back into their juvenile polyp state and repeat this process again and again.