Lobsters Don't Age, But They Do Die
Lobsters are one of a few organisms that seem to exhibit negligible senescence. That is, they don't appear to age in the traditional sense of the word. For as long as they live, they continue to grow and reproduce, without showing the signs of feebleness you would expect in an elderly animal. However, they are not immortal. Lobsters can die in a number of ways, and many of them perish at the hands of humans. Others die when they become too big to muster the energy to moult their shells. (A bigger body size means more energy expenditure.) Some very old lobsters who find it difficult to moult can also contract bacterial infections that kill them.
from Earth Unplugged
Key Facts In This Video
Giant tortoises can live to be more than 250 years old. (0:59)
Lobsters don't exhibit any traditional signs of aging, and can live for more than a century. (1:39)
The "immortal jellyfish" can revert from its free-swimming medusa stage to its "younger" polyp stage. (2:59)