There are some animal species that, for unknown reason, are immortal. Unless an external force does them in, they could theoretically live forever. Here is the list:

1. The sea anemone is an immortal animal. Although it looks more like a brainless plant, it is an animal and defies everything we know about mortality. As sea anemone ages, it simply grows bigger. Unfortunately, they get wiped out at around age 80 by heat, water pollution, infections and collectors.

2. Lobsters don’t grow old and die. In fact, as far as scientists can tell they only die of external causes. They have no brain, and its central nervous system is about as simple as an insect. Lobsters don’t experience any change in metabolism or body-function as they get older. A one-hundred-year-old lobster will even continue eating, moving, procreating and growing. After a couple-hundred years, they can be the size of a large dog.

3. Aldabra giant tortoises is immortal. The males can weigh nearly 800 pounds. They eat vegetation. The oldest confirmed age of an Aldabra tortoise is 255 years, but some may have lived to be twice that age.

4. A rougheye rockfish is an immortal animal. They can live to be 200 years old or more. It grows to a maximum of about 38 inches in length, with the IGFA record weight being 14 lb 12 oz.

5. The hydra is a nearly microscopic simple freshwater animal and it is immortal. Every single cell in the hydra’s tiny body is constantly dividing and rejuvenating. Any injured, polluted or defective cells are diluted by the thousands of others. Because they are constantly replenishing their living cells, hydras do not age.

Although, in theory the above animals are immortal, environmental conditions eventually destroy every living “immortal” animal.