Bivalves-first molluscs (my cladogram)

Ken Kinman kinman at HOTMAIL.COM
Wed Aug 28 03:08:18 CDT 2002

      The debate over my "bivalves-first" hypothesis continues on the
molluscalist newsgroup.  Below is a cladogram with synapomorphies for my
proposed subclades of Mollusca according to my tree topology (upside down
from the way it has long been taught).
                    -------- Ken
>Dear All,
>    I hope that someone will indeed run the test which Dr. Lindberg
>suggested (I don't have the necessary literature yet).  And perhaps also
>plug in the MESENTOBLAST data as well (which is one of the newest
>phylogenetic characters now being used).  Thus I am putting sacoglossans in
>a clade with their euthyneuran descendants, and then streptoneurans alone
>("real torsion" clade) splitting off next----a few primitive streptoneurans
>might still develop the mesentoblast at the 24-cell stage, but the vast
>majority apparently delay such "4d formation" until about 40 or 63 cells.
>Polyplacophora apparently delay even longer (72-cell stage).
>     The big question in my mind is whether protobranch bivalves develop
>their mesentoblast at the 24-cell stage (I haven't been able to find out
>yet).  I have added this character to the synapomorphy list below.  Anyway,
>perhaps the new popularity of "mesentoblast timing" as a character will
>make the skeptics at least a  bit less skeptical of my hypothesis?   The
>dinosaur researchers laughed their heads off (on DML) when I proposed
>oviraptorosaurs were closely related to confuciusornithid birds, but then
>Maryanska et al., 2002, published a cladistic analysis which independently
>came up with the same conclusion.  Will I be that lucky with molluscs?
>We'll just have to wait and see.  I am thus accustomed to having my methods
>branded as "unscientific", especially by "strict" cladists.   :-)
>      ----- Cheers,  Ken Kinman

>>\________ Protobranchia
>>  \________ Lamellibranchia
>>  2\
>>    \___________ EUTHYNEURA     \           \________Cephalopoda
>>     3\
>>       \___ STREPTONEURA (real torsion) >>       4\
>>         \_______ Triblidia
>>         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 ---> 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?
>>    MESENTOBLAST 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.
>Dr. Lindberg wrote (on molluscalist):
>>Kinman has proposed that Sacoglossa may be more closely related to
>>bivalves than other gastropods or are the first (semi-torted) gastropods
>>and maintain the plesiomorphic bivalved-shell.  To test the Kinman
>>hypothesis take the bivalve and gastropod character states from the Ponder
>>& Lindberg (1997) analysis, score your favorite sacoglossan taxon for the
>>same characters, enter the matrix, and hit return.  I look forward to
>>seeing any tree that has a Sacoglossa + Bivalve clade or the Sacoglossa at
>>the base of a gastropod clade.  If such a tree cannot be found, we must
>>reject the Kinman hypothesis and move on to another topic.

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