Taxacom: Mollusca trees (as well as Arthropoda) seem to still suffer from misrooting
Kenneth Kinman
kinman at hotmail.com
Sun Sep 11 18:26:11 CDT 2022
2022
Dear All,
I am very concerned that zoologists (and malacologists in particular), after decades, continue to totally ignore the evidence that the first molluscs were Bivalvia, in spite of the fact that they have the most primitive nervous systems, no radula, no head, and other primitive morphology. Even after I discovered this back in 2002, I eventually found that Thomas Cavalier-Smith (on page 235 of his 1998 Classification of life) had divided Phylum Mollusca into two Subphyla: (1) Bivalvia (marked as probably paraphyletic) and (2) Glossophora (molluscs with a radula and head). On page 242, he says: "I argue that all Lophozoa are ancestrally non-cephalized and that the Bivalvia among the molluscs and the tubicolous Operculata among the annelids are closer to the ancestral state than their more cephalized relatives."
I obviously very strongly agree with Cavalier-Smith. And here we are decades later, and most malacologists still believe that bivalves are a derived Class of molluscs that lost their radulae and heads. We need to start "thinking outside of the box". Molecular trees for molluscs will probably give us the correct phylogeny if they are ever properly rooted. The cladogram below (posted here in 2002 and again in 2017) show just some of the morphological evidence I have found that refutes misrooted molecular trees. IMPORTANT QUESTION: If chitons are so primitive, why haven't we found any in the Early Cambrian along with Bivalvia? Maybe chitons or their stem-group simply didn't exist. On the other hand, Bivalvia probably existed well before the Early Cambrian, but were probably very small (and worse yet, soft shelled due to ocean chemistry during the Pre-Cambiran).
----------------Ken Kinman
Thomas Cavalier-Smith, 1998. "A revised six-kingdom system of life", Biol. Rev.
73 (3):203-266.
________________________________
From: Kenneth Kinman <kin... at hotmail.com> Sent: Wednesday, November 22, 2017 11:32 AM To: taxa... at mailman.nhm.ku.edu; Kenneth Kinman Subject: Were bivalves the first molluscs to evolve?
Dear all,
I was reading an article on the evolution of brains, and the author says
"Meanwhile, bivalves possess just simple nerve nets. You might think that
bivalves came first, while the cephalopods emerged later, because simple brains
should, in theory, predate complex brains." But he then says that DNA tells a
different story (and that is what malacologists continue to be taught to this day).
I'm still of the opinion that cladograms of Phylum Mollusca could very
well be mis-rooted, and that bivalves (with their simple nerve nets) did come
first. Below is the cladogram that I presented here on Taxacom way back in
August 2002. And below that the characters upon which this branching pattern
is based. Are there any obvious errors in this branching pattern, and if not,
could it be that molecular phylogenies for Mollusca are still mis-rooted?
----------Ken
________________________________
\________ Protobranchia (bivalves)
1\
\________ Lamellibranchia (bivalves)
2\
\___________ EUTHYNEURAN gastropods
\ \________Cephalopoda
3\
\___ STREPTONEURAN gastropods (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 (isn't
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://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fio9.gizmodo.com%2Fhow-did-brains-evolve-1653897356&data=05%7C01%7Ctaxacom%40lists.ku.edu%7C9d52312dd89340ba1a5608da944d03e3%7C3c176536afe643f5b96636feabbe3c1a%7C0%7C0%7C637985355742140577%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=hr8PjKlRoFcuQ7L4JOv9K%2Fej4be0KXekzBXJFMT2gdA%3D&reserved=0
[https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fi.kinja-img.com%2Fgawker-media%2Fimage%2Fupload%2Fs--qbRAJ4mk--%2Fc_fill%2Cfl_progressive%2Cg_center%2Ch_450%2Cq_80%2Cw_800%2Ftgtftblcjzufzhgapq4u.jpg&data=05%7C01%7Ctaxacom%40lists.ku.edu%7C9d52312dd89340ba1a5608da944d03e3%7C3c176536afe643f5b96636feabbe3c1a%7C0%7C0%7C637985355742140577%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=A2wMxfiF1Ptf9%2Bk%2Fl6mAXcepQ9oxbezWySi3bwJy2fQ%3D&reserved=0]<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fio9.gizmodo.com%2Fhow-did-brains-evolve-1653897356&data=05%7C01%7Ctaxacom%40lists.ku.edu%7C9d52312dd89340ba1a5608da944d03e3%7C3c176536afe643f5b96636feabbe3c1a%7C0%7C0%7C637985355742140577%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=hr8PjKlRoFcuQ7L4JOv9K%2Fej4be0KXekzBXJFMT2gdA%3D&reserved=0>
How Did Brains Evolve? -
io9<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fio9.gizmodo.com%2Fhow-did-brains-evolve-1653897356&data=05%7C01%7Ctaxacom%40lists.ku.edu%7C9d52312dd89340ba1a5608da944d03e3%7C3c176536afe643f5b96636feabbe3c1a%7C0%7C0%7C637985355742140577%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=hr8PjKlRoFcuQ7L4JOv9K%2Fej4be0KXekzBXJFMT2gdA%3D&reserved=0> 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 ...
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