Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: paul.fr on 08/06/2007 10:35:30
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being kind and gentle, i have never wished to do this. but have heard that it's true! is it?
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No that is not true, the only reason the worm wriggles after you cut it in half is because its nerves are still twitching. if i got a very large knife, and cut you in half, your arms could still move, not much, and so could your legs
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Depends what you mean by worm. The word 'worm' actually applies to a number of phyla of invertebrate animals, including the Annelids (earthworms, polychaetes, leeches), Platyhelminthes (flatworms, tapeworms), Nematodes(roundworms) and Nemerteans (ribbon worms).
The common earthworm, the one you probably find in your garden, is an Annelid worm...and no it won't survive you chopping it, let alone turning into two worms (even though it is made up of repeating segments). Many of the free-living (non-parasitic) flatworms (P: Platyhelminthes, C:Turbellaria) are capable of regenerating wounded tissue and, reproducing asexually by binary fission, so being cut in half can result in two clones. Actually, experiments on Turbellarians involving various incomplete cuts into the worm have resulted in individuals developing two heads, or two tails etc. Some of the parasitic worms are capable of budding off reproductive segments...contributing to their great success as parasites inside the bodies of a variety of host animals. As for the Nemerteans, well I can't quite remember, and my books are too far away from me to check right now, so I might check that up later.
What you might find interesting though, is that starfish are quite capable of regeneration from bits of starfish ie. they can grow replacement arms when arms are lost (aka eaten), or grow an entire body from the one arm.
An interesting story from the southern coast of Australia involves a pest species of starfish, the Northern Pacific starfish. The species has been the cause of the destruction of coral habitat and competition with native marine species since it was brought into Aust waters by foreign fishing vessels. The initial reaction by the Government to the invasion of the species was to pay divers to head out to sea and tear up as many of the starfish as possible, thinking that would kill them (the starfish, that is). Unfortunately the result of that exercise was a further expansion of the starfish population...and that approach has luckily since been abandonned.
For your information, the species continues to thrive in the bay and currently, as far as I've been told, our most effective strategy to controlling its numbers is to discard (in bins etc.) any individuals encountered.
There's something for you to think about. ;)
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Following up on the Nemertean bit, there are a number of species known to be able to regenerate from body fragments and undergo fission. However the majority of species lack these abilities.
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semi related:
dissecting an earthworm... most boring science lab ever!!!
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semi related:
dissecting an earthworm... most boring science lab ever!!!
...hey, but watching the girl in the next seat squeal all lab class about it was pretty entertaining.
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I heard that each segment of a tapeworm can grow to be a full worm after being cut off. Is that true?
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Planaria are legendary for their regenerative capacity after injury.
Some chemicals or electric fields can interfere with their regeneration, producing planaria with 2 (or more) heads.
See: https://en.wikipedia.org/wiki/Planarian#Regeneration
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What about what I asked? Taenia solium or Taenia saginata?