[Taxacom] Tardigrades ----> to Nematodes
kennethkinman at webtv.net
Tue Feb 16 14:34:45 CST 2010
Well, this hypothesis is based on science, but looking at the
science from a different perspective (which I hope will bear fruit).
Too many still have the old "worms are simple and primitive" mindset.
Actually the vast majority of worm taxa are probably secondarily
As for where tardigrades got the moss gene, that is easy.
Tardigrades use their stylets to puncture the cells of mosses and then
they feed on the cell contents (including moss DNA). Tardigrades no
doubt invaded land by feeding and living on mosses and/or algae.
Acquiring the trehalose genes would have been a bonus, since
cryptobiosis is an excellent survival strategy. Nematodes also feed on
mosses and could have acquired such genes directly from their hosts as
well. But nematodes are so similar to tardigrades in many ways that it
is more parsimonious that they are tardigrade descendants and inherited
the genes directly from tardigrade ancestors. Studying their whole
genomes should shed light on that.
Anyway, I am not going to hold my breath waiting for nematode
fossils to be discovered from the Cambrian. More likely that they arose
in the Devonian or after.
Michael Reuscher wrote:
Wow, sounds fascinating. I am only wondering if this is based on science
or a fanciful mind. How did the tardigrades acquire the moss gene ?
> Dear All,
> Isn't it interesting that tardigrades and nematodes >are among
> few animals able to enter cryptobiosis, especially when >threatened by
> extreme desiccation. I would suggest that some clade of >tardigrades
> acquired genes for the production of trehalose sugars from >primitive
> land plants (such as mosses). Both groups would have >faced the same
> problem of desiccation as they invaded land environments >during the
> early Paleozoic.
> I propose that tardigrades in turn passed these >"trehalose
> on to their nematode descendants, thus enabling them to >also take
> advantage of cryptobiosis as a survival strategy. >Something to look
> when comparing nematode and tardigrade genomes.
> --------Ken Kinman
> P.S. If tardigrades evolved from arthropods, as I >suspect, did they
> evolve from crustaceans or from chelicerates??? Both of >these
> groups give rise to terrestrial forms with reduced number >of legs.
> Modern tardigrades have four pairs of legs like many >arachnids, but
> known fossil tardigrades from the Cambrian of Siberia were >apparently
> hexapodous. But then again, I suspect hexapody may have >arisen
> independently more than once from crustaceans. Therefore, >the exact
> number of legs may not be definitive, except that perhaps >reduction
> or 4 pairs of legs may somehow be particularly >advantageous on land
> given the high diversity of hexapods and arachnids on >land.
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