question: How come lobsters are semi-immortal, while shrimp have short lives?
comment: Humans and chimp have a common ancestor and very much look alike. Yet chimp are immune to Alzheimer and we are not. Why ? We don't really know, but two different species even if they look very similar can have a completely different physiology.
passages: 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 immortal in the traditional sense, as they are significantly more likely to die at a shell moult the older they get (as detailed below).
   Section::::Organisms.: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. Similar cases include hydrozoan "Laodicea undulata" and scyphozoan "Aurelia" sp.1.
  
  Section::::Organisms.:Lobsters.
   Their longevity may be due to telomerase, an enzyme that repairs long repetitive sections of DNA sequences at the ends of chromosomes, referred to as telomeres. Telomerase is expressed by most vertebrates during embryonic stages but is generally absent from adult stages of life. However, unlike vertebrates, lobsters express telomerase as adults through most tissue, which has been suggested to be related to their longevity. Contrary to popular belief, lobsters are not immortal. Lobsters grow by moulting which requires a lot of energy, and the larger the shell the more energy is required. Eventually, the lobster will die from exhaustion during a moult. Older lobsters are also known to stop moulting, which means that the shell will eventually become damaged, infected, or fall apart and they die. The European lobster has an average life span of 31 years for males and 54 years for females.
   BULLET::::- "Turritopsis dohrnii", a jellyfish (phylum Cnidaria, class Hydrozoa, order Anthoathecata), after becoming a sexually mature adult, can transform itself back into a polyp using the cell conversion process of transdifferentiation. "Turritopsis dohrnii" repeats this cycle, meaning that it may have an indefinite lifespan. Its immortal adaptation has allowed it to spread from its original habitat in the Caribbean to "all over the world".
  
  BULLET::::- "Hydra" is a genus belonging to the phylum Cnidaria, the class Hydrozoa and the order Anthomedusae. They are simple fresh-water predatory animals possessing radial symmetry.
   Section::::Non-human biological longevity.
  
  Currently living:
  
  BULLET::::- A -year-old member of the species "Pinus longaeva": Oldest known currently living non-clonal tree.
  
  BULLET::::- Methuselah: 4,800-year-old bristlecone pine in the White Mountains of California, the second oldest currently living non-clonal tree.
  
  Non-living:
  
  BULLET::::- Possibly 250-million year-old bacteria, "Bacillus permians", were revived from stasis after being found in sodium chloride crystals in a cavern in New Mexico.
  
  BULLET::::- The quahog clam ("Arctica islandica") is exceptionally long-lived, with a maximum recorded age of 507 years, the longest of any animal. Other clams of the species have been recorded as living up to 374 years.
   Cheloniologists have somewhat recently discovered that chelonians' organs display negligible senescence. This discovery has prompted researchers to do more investigation into the chelonian genome and its impacts on longevity.
  
  Section::::Phylogeny of extant chelonians.
  
  The following phylogeny of extant chelonians is based on the work of Crawford et al. (2015) and Guillon et al. (2012).
  
  Section::::Conservation of chelonians.
   Section::::Longevity.
  
  Lobsters live up to an estimated 45 to 50 years in the wild, although determining age is difficult. In 2012, a report was published describing how growth bands in calcified regions of the eyestalk or gastric mill in shrimps, crabs and lobsters could be used to measure growth and mortality in decapod crustaceans. Without such a technique, a lobster's age is estimated by size and other variables; this new knowledge "could help scientists better understand the population and assist regulators of the lucrative industry".
   Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth's life-forms, including the bristlecone pine at 5062 years or 5067 years, invertebrates like the hard clam (known as "quahog" in New England) at 508 years, the Greenland shark at 400 years, various deep-sea tube worms at over 300 years, fish like the sturgeon and the rockfish, and the sea anemone and lobster. Such organisms are sometimes said to exhibit negligible senescence. The genetic aspect has also been demonstrated in studies of human centenarians.
   BULLET::::- Rougheye rockfish ("Sebastes aleutianus") – 205 years
  
  BULLET::::- Ocean quahog clam ("Arctica islandica") – 507 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.
  
  Section::::Organisms.:Bacteria and some yeast.
   BULLET::::- The larvae of skin beetles undergo a degree of "reversed development" when starved, and later grow back to the previously attained level of maturity. The cycle can be repeated many times.
  
  Section::::Revived into activity after stasis.
   BULLET::::- Flatworms, or Platyhelminthes, are known to be "almost immortal" as they have a great regeneration capacity, continuous growth and binary fission type cellular division.
  
  BULLET::::- Lobsters are sometimes said to be biologically immortal because they don't seem to slow down, weaken, or lose fertility with age. However, due to the energy needed for moulting, they cannot live indefinitely.
   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 longevity may be due to telomerase, an enzyme that repairs long repetitive sections of DNA sequences at the ends of chromosomes, referred to as telomeres. Telomerase is expressed by most vertebrates during embryonic stages, but is generally absent from adult stages of life. However, unlike most vertebrates, lobsters express telomerase as adults through most tissue, which has been suggested to be related to their longevity. Telomerase is especially present in 'Green Spotted' lobsters - whose markings are thought to be produced by the enzyme interacting with their shell pigmentation Lobster longevity is limited by their size. Moulting requires metabolic energy and the larger the lobster, the more energy is needed; 10 to 15% of lobsters die of exhaustion during moulting, while in older lobsters, moulting ceases and the exoskeleton degrades or collapses entirely leading to death.
   The evolutionary theorist George Williams wrote, "It is remarkable that after a seemingly miraculous feat of morphogenesis, a complex metazoan should be unable to perform the much simpler task of merely maintaining what is already formed."
  
  Section::::Variation among species.
  
  Different speeds with which mortality increases with age correspond to different maximum life span among species. For example, a mouse is elderly at 3 years, while a human is elderly at 80 years. 
   BULLET::::- "Zoo" season 2 episode 6 "Sex, Lies and Jellyfish" – The team searches for immortal jellyfish to find a cure for animal mutations.
  
  BULLET::::- Wild Kratts Videos "Meeting the Immortal Jellyfish" – During the rescue of the Bowhead whale from Zach, Martin and Chris are thrown from the Tortuga, ending up in the Sea of Japan with a group of jellyfish. But these jellyfish are different. They're called the Immortal jellyfish and can live forever. With the help of Aviva, Martin and Chris activate with Immortal jellyfish powers and soon discover the highs and lows of living forever.
   The rate of ageing varies substantially across different species, and this, to a large extent, is genetically based. For example, numerous perennial plants ranging from strawberries and potatoes to willow trees typically produce clones of themselves by vegetative reproduction and are thus potentially immortal, while annual plants such as wheat and watermelons die each year and reproduce by sexual reproduction. In 2008 it was discovered that inactivation of only two genes in the annual plant "Arabidopsis thaliana" leads to its conversion into a potentially immortal perennial plant. The oldest animals known so far are 15,000-year-old Antarctic sponges, which can reproduce both sexually and clonally.
   Lifespan: For sexually reproducing planaria: "the lifespan of individual planarian can be as long as 3 years, likely due to the ability of neoblasts to constantly replace aging cells". Whereas for asexually reproducing planaria: "individual animals in clonal lines of some planarian species replicating by fission have been maintained for over 15 years".
  
  They are "literally immortal."
  
  Section::::Attempts to engineer biological immortality in humans.
   The metanauplius of "H. americanus" is long, transparent, with large eyes and a long spine projecting from its head. It quickly molts, and the next three stages are similar, but larger. These molts take 10–20 days, during which the planktonic larvae are vulnerable to predation; only 1 in 1,000 is thought to survive to the juvenile stage. To reach the fourth stage – the post-larva – the larva undergoes metamorphosis, and subsequently shows a much greater resemblance to the adult lobster, is around long, and swims with its pleopods. At this stage, the lobster's claws are still relatively small so they rely primarily on tail-flip escapes if threatened.
   There are many species where scientists have seen no increase in mortality after maturity. This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age.
   BULLET::::- The Antarctic sponge "Cinachyra antarctica" has an extremely slow growth rate in the low temperatures of the Southern Ocean. One specimen has been estimated to be 1,550 years old.
  
  BULLET::::- A specimen, "Ming" of the Icelandic cyprine "Arctica islandica" (also known as an ocean quahog), a mollusk, was found to have lived 507 years. Another specimen had a recorded lifespan of 374 years.
   Cameron also describes how businessman John Risley discovered that lobsters "essentially go dormant in icy water" enabling his company to store them for up to a year by putting them into individual plastic trays stacked in "huge racks which reach clear to the ceilings of the cavernous holding rooms" and pumping 24,000 gallons of chilled sea-water per hour through the trays. "At that temperature," Cameron notes, "lobsters do not eat, grow or moult, but they retain their weight, their texture and their taste, drawing only on the nutrients in their blood." He adds that Risley began airlifting his steady supply of lobsters to cities all over the world transforming his company from its beginnings "as a single roadside lobster stand" into "a corporate empire."
   BULLET::::- The tuatara, a lizard-like reptile native to New Zealand, can live well over 100 years. Henry, a tuatara at the Southland Museum in New Zealand, mated for the first time at the estimated age of 111 years in 2009 with an 80-year-old female and fathered 11 baby tuatara.
   Almost all organisms senesce, including bacteria which have asymmetries between "mother" and "daughter" cells upon cell division, with the mother cell experiencing aging, while the daughter is rejuvenated. There is negligible senescence in some groups, such as the genus "Hydra". Planarian flatworms have "apparently limitless telomere regenerative capacity fueled by a population of highly proliferative adult stem cells." These planarians are not biologically immortal, but rather their death rate slowly increases with age. Some species exhibit "negative senescence", in which reproduction capability increases or is stable, and mortality falls, with age, resulting from the advantages of increased body size with age.
   Section::::Life cycle.:Biological immortality.
  
  Most jellyfish species have a relatively fixed life-span, which varies by species from hours to many months (long-lived mature jellyfish spawn every day or night; the time is also fairly fixed and species-specific). The medusa of "Turritopsis dohrnii" is the only form known to have developed the ability to return to a polyp state, by a specific transformation process that requires the presence of certain cell types (tissue from both the jellyfish bell surface and the circulatory canal system).
   Section::::Description.
   BULLET::::- "Heterocoptis guaicanamarensis" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis guitarti" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis jovai" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis mellacea" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis morenoi" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis najasaensis" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis parallela" (Torre, 1912)
  
  BULLET::::- "Heterocoptis rubiola" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis salvatoris" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis sanchezi" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis sublapidea" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis tabacaria" Torre & Bartsch, 2008
  
  BULLET::::- "Heterocoptis whittami" Torre & Bartsch, 2008
  
  BULLET::::- "Idiostemma alfredoi" Franke & Fernández Velázquez, 2007
  
presuppositions: Similar looking species have the same physiology. If lobsters are semi immortal, than a similar species, shrimp should also have a similar trait.
corrections: Two species can have different physiology while looking similar. Two species can have completely different physiology even they look similar.
raw_presuppositions: Similar looking species have the same physiology. If lobsters are semi immortal, than a similar species, shrimp should also have a similar trait. Lobsters and shrimp should have similar characteristics because of their similar appearances.
raw_corrections: Two species can have different physiology while looking similar. Two species can have completely different physiology even they look similar. Two species can have completely different physiology even they look similar.