Bivalves; and Feduccia newsrelease

Petersen, Mary Elizabeth MEPetersen at ZMUC.KU.DK
Fri Aug 16 22:44:38 CDT 2002


Dear Ken,

Kirk is correct. The bipartite shields of sternaspids are not good
candidates for homologies with shells of molluscs. As far as I know, they
lack calcium carbonate and according to Thomas Bartolomaeus, who broke a
number of knives while trying to section them, in at least some species the
shields have iron. I can personally vouch that although these shields are
often stiff, and sometimes with what appear to be growth rings, the
stiffness is not due to visible calcium (I have not made chemical analyses,
but nothing suggests that such is present), and in some species the shields
are soft and flexible. I looked at most of the material in our collection
when I was writing the sternaspid chapter for the Santa Barbara Taxonomic
Atlas, and apart from becoming aware that nearly all members of the genus
were being reported as Sternaspis scutata (a few as Sternaspis fossor), I
also became aware of a lot of overlooked inter- and intraspecific variation.

That features very siimilar in detail might appear homologous and still not
be so was also made very clear during a talk Lars Orrhage held in 1976. He
showed a number of really beautiful TEM photos of cross sections of chaetae,
while holding a talk on polychaetes and giving the impression - but NOT
directly stating - that the figures were from this group. At the end of the
lecture he casually mentioned that all the TEMs he had shown were of
brachiopods, not polychaetes, although the two could not be told apart on
this feature alone. He suggested that one would hardly claim that the two
were closely related, but even the fine details of the structure were nearly
identical. As you can see, I was very impressed. See Orrhage, Lars. 1973.
Light and electron microscope studies of some brachiopod and pogonophoran
setae with a discussion of the annelid seta as a phylogenetic-systematic
character. ( Journal: Zeitschrift für Morphologie und Ökologie der Tiere 74
(): 253-270

One has to be careful, but I agree that it is good to brainstorm! 

Best regards,

Mary E. Petersen
Zoological Museum, University of Copenhagen
Tel +45-35 32 10 67 - Fax +45-35 32 10 10
E-mail: mepetersen at zmuc.ku.dk
>ooooooooo))))):>

 -----Original Message-----
From:   Ken Kinman [mailto:kinman at HOTMAIL.COM] 
Sent:   Friday, August 16, 2002 9:52 PM
To:     TAXACOM at USOBI.ORG
Subject:        Bivalves; and Feduccia newsrelease

    Yes, an interesting exchange of ideas on the Mollusca list, which I plan
to pursue further (especially on the fossil record).  But there are also the
semantic quibbles to sort through so that everyone understands one another. 
     I've learned that bivalves are not technically "headless", just
buccal-less (in any case, I still think it's probably primitive rather than
secondary).  And bryozoan cyphonautes larvae might not technically have
"shells"----I guess "valves" is more accurate, but my main point is that
they are probably homologous to bivalve shells.  An entoproct larva with
cyphonautes-type valves would be a great model for a bivalve ancestor.  I
agree with Nielsen that entoprocts and ectoprocts are closely related,
although I totally reject his belief that these two groups form a
holophyletic clade.
     And however the xenoturbellid debate turns out is not really all that
central to my arguments overall.  More importantly, if a typical bivalve can
evolve into something like a shipworm, then bivalves could also evolve into
worms which have lost the shells altogether (especially sipunculids, but
perhaps other spiralian worms as well). Could nemertines or some flatworms
actually be very-derived bivalve "slugs"?   If snails can do it, why not
bivalves?  Who knows!!??  I am particularly interested in the shells of
sternaspid polychaetes (perhaps remnants that offer a clue that polychaetes
might have evolved from bivalves??).
     Should be interesting to see w hat comes out of all this brainstorming
and exchange of ideas.  Reminds me of something Darwin once wrote, something
like "without imagination, there is no true and good science".  I like that
point of view.
            ---- Cheers,   Ken
P.S.  For those of you interested in birds and dinosaurs, Alan Feduccia is
in the news again.  See his press release at this URL address:

http://www.unc.edu/news/newsserv/research/feduccia081402.htm

*****************************************
>From: Barry Roth <barry_roth at YAHOO.COM>
>Reply-To: Barry Roth <barry_roth at YAHOO.COM>
>To: TAXACOM at USOBI.ORG
>Subject: Re: -ops family names (plus bivalves)
>Date: Fri, 16 Aug 2002 10:25:07 -0700
>
>In case this sounds like an "up against entrenched authority" spin on the
>transactions over on the Mollusca list, as a participant in both lists, I
>see it somewhat differently.  Ken's initial post was met with serious,
>thoughtful responses, including mention of the fact that the idea of
>Bivalvia as a possibly basal group within (or next to) Mollusca has been
>floated before.  The posts pointed out difficulties with the notion (which
>would have to be overcome before it was adopted as a convincing model), and
>the fact that one of Ken's proffered lines of evidence (a thesis concerning
>the "worm" Xenoturbella) has proven problematic on further study.  I'm not
>sure that the participants have yet achieved any sort of reciprocal
>illumination -- that happens rarely in these settings -- but I was glad to
>see some substantial postings on a list that for weeks at a time often
>contains little of general interest (big surprise). :-)
>Barry
>  Ken Kinman wrote:P.S. By the way, discussions about bivalves and
>molluscan evolution are >taking place on the "molluscalist" newsgroup
through UC-Berkeley. So I >guess I'll get back to that debate, since the
"bivalves-first" hypothesis >is >meeting with stiff resistance (no big
surprise). :-)
>
>
>---------------------------------
>Do You Yahoo!?
>HotJobs, a Yahoo! service - Search Thousands of New Jobs



_________________________________________________________________
Chat with friends online, try MSN Messenger: http://messenger.msn.com




More information about the Taxacom mailing list