Animal Kingdom Question 709
Question: Assertion : Ascidians undergo retrogressive metamorphosis. Reason : Metamorphosis involves transformation of an active form into inert, sedentary form.
Options:
A) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
B) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
C) If the assertion is true but the reason is false
D) If both the assertion and reason are false
Show Answer
Answer:
Correct Answer: A
Solution:
Metamorphosis of the ascidian larva is unique and begins almost explosively.
The tadpole gets attached vertically to the substratum by its adhesive papillae, it stands erect with tail upward, then it begins a degenerate or retrogressive metamorphosis by which it attains the adult condition.
Following changes occur in metamorphosis - (i) Tail along with its structures disappears.
(ii) Four ectodermal ampullae arise from the trunk which firmly anchor the larva to the substratum.
(iii) The atrial cavity as well as pharynx enlarge in size.
(iv) The central nervous system begins to decrease.
(v) Gonads arise from mesenchyme.
(vi) Adhesive papillae and ectodermal ampullae are lost.
(vii) Test increases in thickness and may form foot.
These changes result in the formation of an inert sessile and degenerate adult in which the chordate characters except gill clefts, are lost.
This type of metamorphosis is called retrogressive metamorphosis.
BETA
