Bivalves-first molluscs (my cladogram)
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).
> 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
>> \________ Lamellibranchia
>> \___________ EUTHYNEURA \ \________Cephalopoda
>> \___ STREPTONEURA (real torsion) >> 4\
>> \_______ Triblidia
>> \______ 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 ---> 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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