Chapter 23: Question 4

In debating the question of chordate origins, zoologist eventually agreed that chordates must have evolved within the deuterostome assemblage rather than from a protostome group as earlier argued. What embryological evidences support this view?

Chordates share characteristics with deuterostomes such as: radial clevage, an anus derived from an opening of secondary origin, and a coelom primitively formed by fusion of enterocoelous pouches (except in vertebrates in which coelom formation is schizocoelus, but independently derived, as an accomodation for their large yolks).

molecular data shows that the chordate ancestor was free swimming. Nathan Tingler

Zoologists have also studied the embryonic developmentof deuterostomes.

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