The fastest contraction in the microworld
by Wim van Egmond
|The pictures show Spirostomum ambiguus stretched (left) and contracted (right)|
|The genus Spirostomum contains
some of the largest Ciliates.
The species pictured on this page, Spirostomum
ambiguum, can grow to to a size of more than 4
millimetres. It can therefore be seen without the help of
a microscope. When observed swimming in a little jar of pond water it looks
like a little worm. Only with the help of a microscope
you can see that it is a ciliate. The cell of this
unicellular is totally covered with hairlike 'cilia'. On
the picture you can see the rows of cilia running like a
spiral along the body.
One of the remarkable things of Spirostomum is the way it can contract. The organism can contract it's body to 1/4 of it's length in 6-8 millisec which is the fastest contraction known in any living cell. When observing the creature under the microscope it is easy to watch the contraction by gently touching the sample.
Like many large single celled organisms (giant amoebas, or Stentor: the trumpet animalcule) it has not one nucleus but many. The nucleii form a long strand, like a string of pearls, visible as the lighter structure in the right image.
Spirostomum, like many cilates, feeds on bacteria. They are swept into the mouth opening with a row of specialized fused cilia. The mouth opening is very small and can be found on the side of the body.
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© Wim van Egmond 1998
Published in October 1998 Micscape Magazine.
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