Re: Common ancestor of protostomes and deuterostomes
- From: nospam@xxxxxxxxxx (Paul Ciszek)
- Date: Sat, 3 May 2008 13:44:19 -0400 (EDT)
In article <fuemv0$1thr$1@xxxxxxxxxxxxxxxxxxx>, Remus <roamulus@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?
Since prostomes and deuterostomes are both triploblasts, I doubt they
branched separately off of either cnidaria or ctenophora.
There are triploblasts whose gut has only a single opening. So far as
I know, they are all classified as prostomes. Which is the more likely
scenario?
A) On two separate occasions, a triploblast with a blind gut developed
a second opening
B) A triploblast with a two-ended gut changed how it assigned the
functions of the two openings
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