Why do adult urochordates (tunicates) lack notochords, even though larval urochordates have them? Larvae use notochords to .
A) aid in swimming; adults are sessile and thus no longer propel themselves.
B) stiffen their bodies; in adults, the notochord is replaced by a column of bone.
C) induce tissue differentiation; in adults, tissue is already differentiated.
D) organize their nervous systems; adults' nervous systems are fully developed and do not change.

Option A

Explanation:

A tunicate is marine invertebrate animal  which is a part of chordates. They have notochords and dorsal nerve chord. The subphylum of the organism is called as Urochordata.

The adult urochordates lack notochord but the larval stage of the urochordates have notochord. This is because it helps in swimming of the organism which is required only at the larval stage.

The adult stage of the tunicates is sessile and they do not swim so they do not require notochord.

tissue

explanation:

it is actually formed by geoup of cells which is tissue