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A group of researchers procured some fish-like animals and upon investigation the following characters were observed : A…

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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 ?

[NEET 2026]

a

Exocoetus sp.

b

Branchiostoma sp.

c

Petromyzon sp.

d

Scoliodon sp.

✓ Correct answer: c)

Petromyzon sp.

Explanation
  • The given organism shows primitive jawless vertebrate characters typical of cyclostomes, which represent early-diverging vertebrates.

  • It possesses an endoskeleton made of cartilage, a characteristic feature of early vertebrates lacking true bone.

  • It is ectoparasitic in nature and attaches to fishes using a circular sucking mouth for feeding and blood sucking.

  • It lacks paired fins and scales but bears seven pairs of gill slits for respiration throughout its life cycle.

  • These features are absent in Exocoetus, Branchiostoma, and Scoliodon, which do not show a parasitic sucking mouth condition or jawless state.

  • Hence the organism best fits Petromyzon, a jawless cyclostome fish commonly known as lamprey found attached to marine fishes.

  • Therefore correct identification among given options is Option C which corresponds to lamprey species.

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