NEET 2026 (Phase 1) · BiologyFish classesPrevious Year Question

A group of researchers procured some fish like animals and upon investigation the following characters were observed: A. Endoskeleton was made of cartilage. B. Ectoparasitic; as they were found attached on fish skin with their circular sucking mouth. C. Paired fins and scales were absent, but 7 pairs of gill slits were present. Which of the following species of animals did they consider to fit best with these characters?

Answer: (B) Petromyzon sp.. Petromyzon (Lamprey) is a cyclostome with a cartilaginous cranium and vertebral column, a circular sucking jawless mouth, ectoparasitic habit on fishes, no scales or paired fins, and 6-15 pairs of gill slits (here 7).

  1. A.Scoliodon sp.
  2. B.Petromyzon sp.✓
  3. C.Exocoetus sp.
  4. D.Branchiostoma sp.

Correct Answer

(B) Petromyzon sp.

Solution & Explanation

Petromyzon (Lamprey) is a cyclostome with a cartilaginous cranium and vertebral column, a circular sucking jawless mouth, ectoparasitic habit on fishes, no scales or paired fins, and 6-15 pairs of gill slits (here 7). Scoliodon is a chondrichthyan, Exocoetus a bony fish, and Branchiostoma a cephalochordate, so they do not fit. NCERT Reference: Page 47, line 14-19

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