Re: Common ancestor of protostomes and deuterostomes

Ernest Major wrote:
In message <9f9b3395-1c4b-4b98-81c6-4cb463c3ab32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Craig T <craig.tevis@xxxxxxxxxxxxxxxxxx> writes
On Apr 19, 5:10 pm, Remus <roamu...@xxxxxx> wrote:
I have been reviewing some of the processes of gastrulation and
embryogenesis recently and became interested in what is generally
considered to be the common ancestor of the protostomes and the
deuterostomes. I couldn't really find much on the subject. Is it
generally considered that both branched off from cnidarians
separately, or is there generally considered to be an ancestor of all
bilateria that then specialized to produce the protostomes and the
deuterostomes? Or are even the cnidarians a seperate branch, with the
bilaterians or even both the protostomes and the deuterostomes
branching off from something like the ctenophora?

There's a phylogenic tree at
http://whozoo.org/inverts/animalphylo.htm

It uses findings from Casey Dunn that show ctenophores branching off
before other animal groups. It shows protostomes as a sister group to
deuterostomes. Their common ancestor branched off from the common
ancestor of porifera and cnidarians. I know that the idea of comb
jellies branching off first was a radical split from earlier views,
but I don't know if anything else in this tree is controversial.

To the best of my knowledge it remains an open question as to whether protostomes and deuterostomes collectively comprise the totality of bilaterians, or whether they are bilaterians that are neither protostomes nor deuterostomes. It used to be the case that acoelomates were thought to be such bilaterians, but it is now recognised that at least some acoelomates are secondarily simplified.

But according to the recent common wisdom, acoel flatworms (not most flatworms) are primitely so.

.

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