Question

Tunicates has bilateral symmetry but is not cephalized. What features of this organism' life history do you think contribute to it not sharing the association of cephalization and bilateral symmetry?

Answer 1

Ans: Mostly organisms who are cephalized are also bilateral symmetrical. But this is not the case with Tunicates.

This is because of the retrogressive metamorphosis observed in them.

Tunicate larva has a nerve cord in its tail which is similar to the nerve cord found in vertebrates. But when this larva develops in to an adult it settles at the bottom of the sea or a stone and the tail ( along with nerve cord) is reabsorbed to provide nutrition to the developing adult.

As nerve cord is present in larvae but absent in adult this metamorphosis is called retrogressive metamorphosis.

Because of the absence of nerve cord in adult Tunicates have bilateral  symmetry but don't have cephalization.