Question

Assertion :It is necessary to study the life history of an ascidian to consider it as chordate. Reason: Tadpole larva of ascidians has a notochord that disappears in the adult.

• A. Both assertion and reason are correct and reason is the correct explanation for assertion.
• B. Both assertion and reason are correct but reason is not the correct explanation for assertion.
• C. Assertion is correct but reason is incorrect.
• D. Both assertion and reason are incorrect.

Answer 1

The correct option is A Both assertion and reason are correct and reason is the correct explanation for assertion.

Assertion is correct as ascidians (class-Ascidiacea), commonly known as sea-squirts, are a class of sessile, filter-feeding chordates who live solitarily or colonially inside an extracellular 'tunic.' Adult ascidians bear little resemblance to typical chordates, though clearly exhibit the four fundamental characteristics of the phylum; a dorsal tubular nerve cord, notochord, rudimentary pharyngeal gills slits and a post-anal tail. Therefore it is necessary to study the life history of an ascidian to consider as chordate.

Reason is also correct and correct explanation of assertion as like other chordates, tunicates have a notochord during their early development, but by the time they have completed their larval stages, they have lost all myomeric segmentation throughout the body. As members of the Chordata, they are true coelomates with endoderm, ectoderm and mesoderm. Hence option A is correct.