You chose the ancestor to the Annelida, Mollusca, and Arthropoda
The main structural evidence that the Mollusca, Annelida, and Arthropoda evolved from an ancestor that was not an ancestor to the other animals is that all three groups have all four main traits of protostomes . This means that they hav
e several unique developmental features (click on any feature for an explanation of what it means):
- Schizocoelous
development of the coelom. This is the trait that is
really unique to these three phyla. The rest of the traits probably evolved in earlier ancestors, but are traditionally considered part of the protostome condition, so they are list
ed here.
- The blastopore
develops into the mouth, not the anus
- Spiral cleavage
- Determinate
cleavage
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phylogeny exercise