Question

in which organism did bilateral symmetry begin? select one answer.
flatworms
roundworms
cnidarians
sponges

Explanation:

The cladogram shows that bilateral symmetry (along with 3 germ layers) first appears at the branch leading to flatworms. Cnidarians have radial symmetry, sponges have no symmetry, and roundworms come after the evolution of bilateral symmetry in flatworms.

Answer:

Flatworms