—Tardigrades.

tardigradeslbl

WATER BEAR (Tardigrade)

tardigrade

Schnoot
Half-millimeter-long tardigrade in moss.
PHOTO (electron microscope, color enhanced): Eye of Science/Science Source
[via NatGeo – h/t PZ]

Tardigrades (Phylum: Tardigrada) are also known as water bears or moss piglets. They are teeny, tiny, water-dwelling, eight-legged animals prevalent in moss and lichen. About 1 millimeter (0.039 in) in length when fully grown, they can be seen under a low-power microscope. Tardigrades are able to survive in extreme environments that would kill almost any other animal: they can withstand temperatures from just above absolute zero to well above the boiling point of water, pressures about 6 times stronger than found in the deepest ocean trenches on Earth, ionizing radiation at doses hundreds of times higher than would kill a human, and the vacuum of outer space. They can go without food or water for many years, drying out to the point where they are less than 3% water and suspending their metabolism (cryptobiosis)—then rehydrate, forage, and reproduce. Tardigrades have been found in hot springs, on top of the Himalayas, under layers of solid ice, in ocean sediments, in lakes, ponds, meadows, stone walls and roofs. Usually males and females are present, but some species are parthenogenetic.

WaterbearTardigrade (water bear) Hypsibius dujardini
scanning electron micrograph by Bob Goldstein & Vicky Madden
UNC Chapel Hill

Tardigrades are oviparous (egg-laying), and fertilization is usually external. (A few species have internal fertilization.) When the female molts she lays eggs inside her shed cuticle, which the male then covers in sperm. The eggs hatch in less than two weeks, with the young already possessing their full complement of adult cells. Growth to adult size occurs by enlargement of the individual cells (hypertrophy), rather than by cell division.

See also:

Prof. Bob Goldstein at UNC Chapel Hill discussing tardigrades (NatGeo):

This slideshow, courtesy of Prof. Goldstein’s lab.

Absurd Creature of the Week: The Incredible Critter That’s Tough Enough to Survive in Space. Simon, M., Wired (Mar. 2014).

Sadly, as of this writing we still have not received a reply from Professor Goldstein to our groundbreaking research proposal. It’s like he doesn’t even want to share the Nobel prize with us. ?

tardigrades__________
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