[Taxacom] How did Hurdia use its bizarre carapace?

[Kenneth Kinman]

 Dear All, 
       This is in response to part of a post I made here
over six years (see below).  The long-delayed description of the Hurdia
animal finally got published last year, but I somehow missed it until
now.              
       Noone seems to know what the heck was the purpose
of having that HUGE anterior  carapace. I haven't seen anyone suggest
this, but my immediate reaction was that Hurdia probably enrolled its
body into this carapace when it was threatened.  It would have been a
rather crude and unwieldy type of enrollment (compared to trilobites),
but I see no reason that it wouldn't have worked during the Cambrian
when a lot of experimentation in body plans was occurring.  However, I
just can't see an animal investing so much energy growing and carrying
around such a large structure just for digging around in the sediments
or funneling prey to its mouth (the two common suggestions I've seen
made as to its purpose).      
        Anyway, if Hurdia did enroll in such a fashion, its carapace
would represent to me the remnant of a bivalved ancestry which I
envision as the common ancestor for all ecdysozoans (which would have
externally resembled something like an ostracod, but we won't know what
the body inside those shells looked like until we truly understand the
phylogeny of Ecdysozoa).  It would be nice if we had a "Burgess Shale"
type of locality dating from the Upper Precambrian. 
        -------Ken Kinman                                
-------------------------------------------------------------

 Six years ago (13 September 2004), I wrote on Taxacom: P.S. And don't
be too surprised if the bivalved myxozoans are remnants of a very early
radiation of ecdysozoans (whether they are directly related to nematodes
or not). Remember my post here last year about primitive arthropods
being bivalved? Perhaps there is some method in my "madness" after all??
  Only time will tell, but I find new evidence very encouraging (and I
still have no doubts that Lophotrochozoa is a muddle mess that should be
abandoned!!).   If I am correct, all ecdysozoans had bivalved
ancestors---including the onychophorans and anomalocareans (the latter
would probably be clearly confirmed if new Hurdia specimens were ever
described instead of sitting in someone's museum drawer for well over a
decade).