Question Detail
Question
Which one of the following is not applicable to the retrogressive metamorphosis of ascidian tadpole?
Correct Answer
Option A is the correct answer.
Detailed Explanation
During retrogressive metamorphosis in ascidians (sea squirts), the free-swimming tadpole larva undergoes simplification to become a sessile adult. The notochord dwindles (B), the tail shortens and is absorbed (D), and the animal becomes sessile (C). However, the pharynx does not reduce in size; instead, it greatly expands and develops numerous gill slits to become a highly developed branchial basket for filter-feeding. Thus, reduction of the pharynx is not applicable.
Hint
Contrast the larval and adult structures in ascidians; consider which organ system becomes more developed in the adult for filter-feeding.