Segmentation in different Phyla

[smithy2192]

There has been discussion over whether segmentation was evolved independently in the phyla Arthropoda, Annelida and Chordata. Does anyone know any reasons behind why this hypothesis has come about due to body structure? Is it different functions of the segmentation or just different types of segmentation?

[crunknorris]

Natural Selection.
You kind of answered your own question.
It is to my knowledge that evolutionary trees branch outward. Meaning each phyla would evolve independently. They could evolve convergently if needed though. This could happen for a number of reason. Mostly environmental stress, or preditor prey relationships. Like how Mako sharks evolve convergently with Tuna. Mako sharks and Tuna are both fast swiming fish so they have evolved to have simmilar body plans.
I know that is an example of Covergent evolution within a phyla, but it does happen with species from seperate phyla.

[JackBean]

crunknorris: I think you misunderstood. IMHO the question is, how can you say, that the segmentation evolved AFTER the phyla separation, not before

[crunknorris]

I can see that now. Sorry, about the misunderstanding of the question. That being said Evolution is a fact these days. Those who believe in it also have different opinions on the logistics of the whole process. My advice at this point would to check out some different phylogenic trees. Ones that dispute the opinion that segmentation eveolved after seperation. That being said I do believe there was a certain amount of segmentation that was naturally selected before phyla's seperated, and some after. Which is what helps distingish the different phyla.