[Taxacom] Mollusca & Glossophora
kennethkinman at webtv.net
Thu Mar 12 21:13:18 CDT 2009
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):
\____ STREPTONEURA (real torsion)
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).
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.
Mesentolblast formation occurs
after 63-cell stage.
6. Radular reduction.
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
NOTE: ** indicates that the synapomorphy is subject to reversals
or other modifications down the line.
More information about the Taxacom