Here are some of the most famous examples of animals considered “biologically immortal” or nearly so:

1. Turritopsis dohrnii (Immortal Jellyfish)

• This tiny jellyfish can revert its cells to an earlier stage (a polyp) when stressed or injured.
• Essentially, it resets its life cycle, making it theoretically immortal—though it can still die from disease or predation.

2. Hydra

• A small freshwater organism that continuously regenerates its cells.
• It doesn’t show signs of aging because its stem cells keep dividing indefinitely.

3. Planarian Flatworms

• Known for remarkable regeneration—they can regrow entire bodies from fragments.
• Their stem cells and telomerase activity make them resistant to aging.

4. Certain Bacteria & Archaea

• Some microbes can form spores and survive for millions of years in dormant states.
• They’re not “immortal” in the usual sense but can persist almost indefinitely under the right conditions.

5. Lobsters

• As we discussed, they have active telomerase and don’t show typical aging signs.
• They eventually die from external factors like disease or molting complications.

6. Greenland Shark

• Lives 400+ years, making it the longest-lived vertebrate known.
• Not immortal, but its aging process is extremely slow.