Question

Assertion: Characters of cyclostomes show they are advanced over Amphioxus.
Reason: Cyclostomes have some degenerated characters.
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

Cyclostomes are the living agnathans. The word Cyclostome means round mouth. They have many primitive and some specialized characteristics. Cyclostomes are jawless fishes with horny epidermal structures that function as teeth. The cyclostome fishes include lampreys and hagfishes. They have no proper digestive system. Some of their characters are found similar to Amphioxus.

Complete explanation:
The amphioxus has more primitive characters than cyclostomes. The cyclostomes have advanced characters such as cranium, pro and epinephrine kidneys, secondary notochord and a rudimentary- vertebrae which are absent in amphioxus. Hence the assertion is correct.
Some of the degenerated characters in cyclostomes are the tongue apparatus, rudimentary pair of eyes (hagfish), lack of exoskeleton, small liver and lack of gallbladder and bile duct (lamprey).
Option A: Both assertion and reason are correct but the degenerative characters of cyclostomes are not the reason for them being more advanced than amphioxus.
Option A is incorrect.
Option B: This option is correct as both the assertion and reason are right and reason is not the correct explanation for assertion.
Option B is correct.
Option C: Since reason is given as wrong in this option, it is incorrect.
Option C is incorrect
Option D: Both assertion and reason are given as incorrect here which is wrong.
Option D is incorrect.

Therefore, Option B is the correct answer.

Note:
The body of the cyclostomes is round and elongated like an eel. They lack paired fins. Median fins are present with cartilaginous fin rays. Their skin is soft and smooth, with no scales. The endoskeleton is cartilaginous with lack of bones. They have a single and a median nostril. The digestive system is not developed. The subdivision of cyclostomes includes Petromyzontiformes and Myxiniformes.