Question

Retrogressive metamorphosis is peculiar to
A. Urochordates
B. Hemichordates
C. Cephalochordates
D. All the above.

Answer 1

Hint: Retrogressive metamorphosis is the term that may be defined as when the larva of an organism possesses more advanced character than that of an adult. Larva have better life form than that of the adult and have unique characters.

Complete answer:
Chordates possess some unique characteristics as:
They possess notochord
They have ventral heart
They have paired pharyngeal gill slits
They have post anal tail present in them.
Now let us know something about given options:
Urochordates: they are organisms in which larvae possess tails and adults do not have tails. So, larvae are more advanced than that of adults. They show retrogressive metamorphosis.
Hemichordates: They were later placed in chordates but now they are removed from there. They do not possess chordates like character. They do not possess larva stage so do not show retrogressive metamorphosis.
Cephalochordates: They have tails persistent throughout their life in larva as well as adults. The tail. Thus, larva and adults have the same character. So, they do not show retrogressive metamorphosis.
All of the above: As hemichordates and cephalochordates do not show retrogressive metamorphosis. This option cannot be true.

Our required answer is A) Urochordates.

Note: The adult body of tunicates or urochordates is enclosed within a leathery test or tunic formed of a cellulose like organic substances termed as tunicin, so they are also called as tunicates. They change from better developed larva to less developed adult.