Phylum platyhelminthes (flatworms)

What trait first appeared in Phylum Platyhelminthes? (see the cladogram)  

Bilateral Symmetry

flatworms

class tubellaria

tapeworms

class cestoda

importance bilateral symmetry

allows for the presence of a head, therefore a centralized nervous system

new features

Phylum platyhelminthes has a head and gangila, (primitive brain)

Cephalization

Cephalization is the concentration of nervous tissue and sense organs at the front (head) of the bod

flatworms sturturce

acoelmate, look at picture