(Strongylocentrotus franciscanus) – 200 years Rougheye rockfish (Sebastes aleutianus) – 205 years Ocean quahog clam (Arctica islandica) – 507 years Greenland shark (Somniosus microcephalus) - 250 to 500 years In 2018, scientists working for Calico, a company owned by Alphabet, published a paper in the journal eLife which presents possible evidence that Heterocephalus glaber (Naked mole rat) do not face increased mortality risk due to aging. Bacteria and some yeast Many unicellular organisms age: as time passes, they divide more slowly and ultimately die. Asymmetrically dividing bacteria and yeast also age. However, symmetrically dividing bacteria and yeast can be biologically immortal under ideal growing conditions. In these conditions, when a cell splits symmetrically to produce two daughter cells, the process of cell division can restore the cell to a youthful state. However, if the parent asymmetrically buds off a daughter only the daughter is reset to the youthful state—the parent isn't restored and will go on to age and die. In a similar manner stem cells and gametes can be regarded as "immortal". Hydra Hydras are a genus of the Cnidaria phylum. All cnidarians can regenerate, allowing them to recover from injury and to reproduce asexually. Hydras are simple, freshwater animals possessing radial symmetry and contain post-mitotic cells (cells that will never divide again) only in the extremities. All hydra cells continually divide. It has been suggested that hydras do not undergo senescence, and, as such, are biologically immortal. In a four-year study, 3 cohorts of hydra did not show an increase in mortality with age. It is possible that these animals live much longer, considering that they reach maturity in 5 to 10 days. However, this does not explain how hydras are subsequently able to maintain telomere lengths. Jellyfish Turritopsis dohrnii, or Turritopsis nutricula, is a small () species of jellyfish that uses transdifferentiation to replenish cells after sexual reproduction. This cycle can repeat indefinitely, potentially rendering it biologically immortal. This organism originated in the Caribbean sea, but has now spread around the world. Key molecular mechanisms of its rejuvenation appear to involve DNA replication and repair, and stem cell renewal, according to a comparative genomics study. Similar cases include hydrozoan Laodicea undulata and scyphozoan Aurelia sp.1. Lobsters Research suggests that lobsters may not slow down, weaken, or lose fertility with age, and that older lobsters may be more fertile than younger lobsters. This does not however make them