Question

Which of the following characteristics occurs in urochordate larva, during retrogressive metamorphosis?
A. Loss of notochord
B. Loss of tail
C. Experience reduction of nervous system to a visceral ganglion
D. All of the above

Answer 1

Hint:-The term metamorphosis means a transformation. Metamorphosis refers to a change in appearance, structure and function. The transformation of an individual animal at different stages of development i.e. from hatching to maturity is a metamorphosis.

Complete Answer:-
Retrogressive metamorphosis is a type of metamorphosis, in which case, the larva possesses advanced characters that are lost during the development. The adult may be either sedentary or degenerated with initial characters. Urochordata adults are sedentary but show advanced chordate characters that are lost during metamorphosis.
There are different types of changes that can be noticed in the urochordate larva at the time of retrogressive metamorphosis. In this case, the larva gets attached to the substratum with the help of chin warts, head downward, and tail up. During metamorphosis, rapid growth is seen between the chin warts and mouth and at the same time, there is no growth on the opposite side of the body. Due to rapid growth on one side, the body begins to rotate in such a way that the mouth gradually moves to the upper side and the pharynx becomes enlarged, and the numbers of stigmata increase. Due to retrogressive metamorphosis, the intestine starts to function and an atrial opening is generated on the opposite side of the oral aperture. Both the tail and notochord of the larva are gradually distinguished or lost in the body during metamorphosis and the reduction of the hollow nerve cord into a solid visceral ganglion also happens. Sense organs and statocyst are also lost. So, all the three above given changes occur in the urochordata larvae during retrogressive metamorphosis.
Thus, the right option is D.

Additional information:-
Metamorphosis means transformation that is different changes in appearance, structure, and function through the life cycle of an organism. These changes can occur in an individual animal through its different stages of development i.e. from hatching to maturity. The formation of motile sperm from spermatids also can be considered as a kind of metamorphosis. Metamorphosis is a common characteristic in the life cycle, that is observed in insects and amphibians.

Note:- Metamorphosis refers to a transformation or change in appearance, structure, and function in an individual animal at its different stages of the life cycle. In the case of retrogressive metamorphosis, the larva possesses advanced characters that are lost during development. During retrogressive metamorphosis, a urochordate larva lost its both tail and notochord. Also, its hollow nervous system is reduced to a visceral ganglion.