Final answer:
The main difference between Urochordata and Cephalochordata is that cephalochordates retain a notochord and a dorsal hollow nerve cord throughout adulthood, whereas urochordates only have these structures during their larval stage.Option B is the correct answer.
Step-by-step explanation:
The main difference between Urochordata and Cephalochordata pertains to the presence and persistence of a notochord and neural structures throughout their lifecycle.
Urochordates, like tunicates, possess a notochord and nerve cord only during the larval stage, after which these structures mostly disappear in the adult form. On the other hand, Cephalochordates, including lancelets, retain these features into adulthood, possessing a notochord and a dorsal hollow nerve cord that extends into the head, with no significant development of a distinct brain.
Given this information, the correct option is B) Presence of a notochord in Cephalochordate, as it indicates the distinctive characteristic of having a notochord in the adult stage, which is not seen in adult Urochordata.