I find it very interesting that one can essentially conceptually reverse the accepted evolution of molluscan groups. The only problem is that the fossil record does not support such a reversal, although it is rather scanty.
Allen Aigen
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---------- Original Message ----------
From: Frederick W Schueler <[log in to unmask]>
To: [log in to unmask]
Subject: Re: [CONCH-L] Was HAM just flim-flam?
Date: Mon, 30 Mar 2009 10:24:19 -0400
Thomas Eichhorst wrote:
> I Goggled (Google Books) "ancestral mollusk fossil ham" and the first
> entry that comes up is Lindberg, David R.; Ponder, Winston F.; &
> Haszprunar, Gerhard. “The Mollusca: Relationships and Patterns from
> Their First Half-Billion Years,” /Assembling the Tree of Life/,
> (Cracraft, Joel & Donoghue, Michael J. – eds.), Oxford University Press,
> pp. 252-278.
* I append a message from Taxacom that's an introduction to a recent
discussion of a radical idea of molluscan ancestry. You can follow the
whole thread by following the directions in the footer file.
fred.
------------------------------------------------------------
Bishops Mills Natural History Centre
Frederick W. Schueler & Aleta Karstad
RR#2 Bishops Mills, Ontario, Canada K0G 1T0
on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
(613)258-3107 <bckcdb at istar.ca> http://pinicola.ca
------------------------------------------------------------
-------- Original Message --------
Subject: [Taxacom] Mollusca & Glossophora
Date: Thu, 12 Mar 2009 21:13:18 -0500
From: [log in to unmask] (Kenneth Kinman)
To: [log in to unmask]
CC: [log in to unmask]
Dear All,
I should have noted that I do not advocate using the term
"Lipocephala" instead of Bivalvia or Pelecypoda. However, Lankester's
term Glossophora is a perfectly good clade according my proposed
phylogeny of Mollusca. Some of the synapomorphies for Glossophora were
listed with the Mollusca cladogram which I posted here on Taxacom back
in 2002 (that list of preliminary synapomophies and the cladogram are as
follows, with Glossophora beginning at step no. 2, between
Lamellibranchia and the Euthyneura gastropods):
\________ Protobranchia
1\
\________ Lamellibranchia
2\
\___________ EUTHYNEURA
\ \________Cephalopoda
3\
\____ STREPTONEURA (real torsion)
4\
\_______ Monoplacophora
5\
\______ Polyplacophora
6\
\_______ Aplacophora
1. Veliger larvae evolve.**
Gills become lamellate.
Crystalline style evolves.**
2. Simple radulae evolve.
Thus abandon filter-feeding.
Cleavage becomes unequal.
Buccal development begins.
Adductors reduced from 2 to 1 (or 0).
Unskeletonized gills?
Shells more "opisthobranch"-like.**
Gastropodan muscle fine structure.**
3. Radulae become more complex,
with increasing numbers of
teeth per transverse row.**
Mesentoblast (4d) formation
begins to come after the
24-cell stage (usually 40-63).
4. "Segmentation" arises.**
8 pairs of pedal retractors.
More than 6 pairs of dorsoventral
muscle bundles (DVM).
Over two pairs of ctenidia.**
Radula bolster vesicles increase.
5. Single conch becomes multiple plates.**
Spicules develop (7 rows**).
Even more pairs of DVM (is not
fission as likely as fusion!?)
Musculature develops beneath mantle.
Head appendages lost.
Statocysts lost?
Mesentolblast formation occurs
after 63-cell stage.
6. Radular reduction.
Plates lost.
Muscular foot reduced.
Numbers of ctenidia reduced.
More than 16 prs. of DVM (certainly
no reversal here).
Gametes usually exit via pericardia
(those which don't are probably
basal aplacophorans).
NOTE: ** indicates that the synapomorphy is subject to reversals
or other modifications down the line.
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