[Taxacom] diphyletic/paraphyletic Bivalvia

[Kenneth Kinman]

Dear All,

       The phylogeny of Mollusca that I presented shows a paraphyletic Bivalvia (Protobranchia + Lamellibranchia).  Perhaps this is why some molecular trees for Mollusca have shown a mystifying diphyletic Bivalvia (some bivalves branching off within the Gastropoda.  The complete mitochondrial genome of genus Solemya shows it embedded within the Gastropoda.  And that same paper notes a diphyletic Bivalvia appearing other molecular trees (such as the 18S RNA)---see weblink below.


     There seems to be no explanation for such results, but noone seems to have considered mis-rooting ( choosing the wrong outgroup) to be the problem.   Perhaps more molecular data (especially for the bivalved gastropods, Family Juliidae) could shed light on these problems.


https://bmcgenomics.biomedcentral.com/articles/10.1186/1471-2164-14-409


________________________________


>>
>>\________ 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 ---> 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.

--------------------------------------------------------------------------------
Here's a weblink to the article on the evolution of brains:
  https://io9.gizmodo.com/how-did-brains-evolve-1653897356


[https://i.kinja-img.com/gawker-media/image/upload/s--qbRAJ4mk--/c_fill,fl_progressive,g_center,h_450,q_80,w_800/tgtftblcjzufzhgapq4u.jpg]<https://io9.gizmodo.com/how-did-brains-evolve-1653897356>

How Did Brains Evolve? - io9<https://io9.gizmodo.com/how-did-brains-evolve-1653897356>
io9.gizmodo.com
Humans have asked where we come from for thousands of years, across all cultures. But only recently have we started to address the mystery of the evolution of the ...