What is the smallest animal in the world?

The Tardigrade!

This is a question that many people have answered (incorrectly) on the web.  An animal is a multicellular organism, therefore the answer cannot be an amoeba.  It is not Megaphragma caribea, or fairyfly. The fairyfly is a parasitic wasp that lives on the island of Guadaloupe and feeds off the eggs of other insects. Specimens have been found between 0.10 mm to 0.17 mm in length, which makes it the smallest insect in the world, but there are other animals that are smaller still.  This wasp is smaller than the smallest vertebrate and the smallest mammal, yet all of these are beaten out by a little creature known as a tardigrade.



Tardigrades are also known as water bears or moss piglets.  They range in size from 0.5 mm to less than 0.1 mm in length.  Newly hatched larvae may be 0.05 mm in size.  Tardigrades can survive extremes of temperature and pressure that would kill almost any other animal, ranging from the vacuum of space near absolute zero, to 151 degrees Celcius and pressures of the deepest sea trench.  They can survive about 1000 times more radiation than other animals, and due to their extreme hardiness are encountered from the tops of the Himalayas to the depths of the oceans and from the Arctic to the jungle.

Tardigrada is actually a phylum that contains about 1000 species.  Tardigrada means slow walker, and videos of these animals look like a microscopic bear walking around.

While some species of tardigrades are parthenogenetic, most have both male and female species.  They are oviparous, and usually the male will fertilize the female eggs externally in the moulted shell of the female.  Tardigrades are eutetic, meaning that all adults in each species have the same number of cells.  Tardigrades may have 40,000 cells, some species have fewer.  The young have the same number of cells as adults; tardigrades increase in size by hypertrophy, a process by which an animal increases the size of its existing cells rather than making more cells.

There is a wonderful wiki article about tardigrades here.

Here is a video with rocking music of a waterbear strutting his stuff:

Rotifers may tie in size for the smallest animals.  Finding your own rocking rotifer video is left as an exercise for the reader.


~ by exceptionalanimals on March 23, 2011.

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