[Taxacom] Mollusca & Glossophora

Kenneth Kinman kennethkinman at webtv.net
Thu Mar 12 21:13:18 CDT 2009

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
    \________ Lamellibranchia
      \___________ EUTHYNEURA      
        \              \________Cephalopoda      
          \____ STREPTONEURA (real torsion)    
            \_______ Monoplacophora 
              \______ Polyplacophora 
                \_______ 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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