Anyone here interested in Tardigrades and Arthropod origins?

[Monad]

I've been fascinated by arthopod evolution for a long time but recent models seemed such a radical departure from what I had learnt about Arthropod evolution (the supposed link with Annelids) and at first glance didn't seem to make much sense. In the light of the Ecdysozoan hypothesis it made sense to look for forms that may prove "intermediary" between nematodes (and other Ecdysozoa) and arthropods so I've been searching for information about Tardigrade evolution and molecular phylogeny since Tardigrades seem to have many characteristics that appear intermediary between the two groups. I came across this site which seems to have some intesting evidence and models of how this may have occured:

http://zeldia.cap.ed.ac.uk/tardigrades/Tardigrades.html

there are also some interesting discussions here:

http://www.peripatus.gen.nz/Taxa/Arthropoda/Index.html

http://www.biology.appstate.edu/faculty/dewelwc.htm

Anyone else got any information on these developments? The whole field seems to be in a state of very rapid development at the moment - I'd especially like to know more about the presence of HOX sequences in Ecdysozoa.

[Chris Porter]

While tardigrades have to be my most very favorite micro animal, I know very little about them other than their morphology. My very old invertebrate textbook doesn't even mention them.

Having read the links, I'm still unsure how valid the concept of Ecdysozoans is, not having run across it before. And, just because the mouthparts of a tardigrade are triparate like a nematode pattern, is this something that should only be thought of as having developed once (thus relating nematodes to tardigrades)?

SEM closeups of nematodes can be found here (http://www.denniskunkel.com/advanced_search_result.php?keyword=nematode) and a picture of a tardigrade here. (http://www.denniskunkel.com/advanced_search_result.php?keyword=tardigrade)

[Monad]

Having read the links, I'm still unsure how valid the concept of Ecdysozoans is, not having run across it before. And, just because the mouthparts of a tardigrade are triparate like a nematode pattern, is this something that should only be thought of as having developed once (thus relating nematodes to tardigrades)?

You're right - it's still inconclusive I think but if the Ecdysozoa hypothesis is correct than the Tardigrades certainly make a better model for what a transition between Nematode like organisation and Arthropod like organisation than anything else I can think of so that's why I was looking for more. What might help make things clearer though is a fuller analysis of the HOX sequences of this group and other's in the Ecdysozoa. Incidentally I'm just reading the section in Karl Zimmer's "Evolution" on HOX sequences in Vertebrates and Arthropods and what they might tell us about our common ancestor - that also made me think of Tardigrades for some reason. I strongly suspect that this once little known group is going to be attracting a hell of a lot more attention in the future and about time too. It certainly looks to me like there was a huge diversification of Lobopod-like organisms in the late precambrian and something like a Tardigrade could have been basal to that and a link with other Ecdysozoa (if that hypothesis holds).

[Monad]

Found a very interesting article discussing the Cambrian radiation and early arthropod ancestry.

http://www.google.co.uk/url?sa=t&ct=res&cd=7&url=http%3A//www.earthscape.org/r3/ES14785/ch18.pdf&ei=kCf_QoKGN6vURd6uqEk

and another link:

http://www.science.uva.nl/onderzoek/cepa/JennerSchram02.pdf

found a few about HOX sequences that would have been interesting but they are all on sites where you have to pay a ridiculous amount to read what should be freely available knowledge :(

[premjan]

arthropod larvae are often wormlike, could we say that they are more like nematodes or annelids?

[Monad]

arthropod larvae are often wormlike, could we say that they are more like nematodes or annelids?

Only Holometabolous insects afaik and they are pretty good examples of highly derived larvae - a good tonic to any recapitulationist interpretation I suspect.