A)Radial
B)Bilateral
C)Rotational
D)Discoidal
E)Spiral

A)only a diffuse subepidermal nerve plexus underneath the ventral skin.
B)a simple brain of ganglion cells leading to a ladder-type nerve network.
C)only sensory and motor neurons,but no association neurons.
D)the first complex central nervous system.
E)no cells since they were lost along with other unnecessary systems in parasites.

A)fully mature adults.
B)free-swimming larvae.
C)flagellated,amoeboid larvae.
D)larvae resembling gemmules of freshwater sponges.
E)None of the choices is correct