Question

Which of the following statement is incorrect?

• A. Unpaired nostril is found in Petromyzon.
• B. The body of Petromyzon is devoid of scales and paired fins.
• C. Petromyzon shows catadromous migration.
• D. Petromyzon has suctorial mouth with rasping tongue.

Answer 1

Answer: (C)

Petromyzon (Lamprey) belongs to the class Cyclostomata. Some general characteristics are as follows:

1. On some or the other fishes, all the living members of class Cyclostomata are ectoparasites.
2. For respiration, they have usually 6 to 15 pairs of gills slits in their elongated body.
3. The absence of stomach is seen.
4. Closed circulation is present.
5. Paired fins and scales are not present in the body.
6. A sucking circular mouth is present.
7. Due to the absence of jaws, they are also known as jawless fishes.
8. Cartilaginous cranium and vertebral column are present.
9. Although being marine, they migrate to freshwater for spawning (anadromous migration). Within few days after spawning, they die. After metamorphosis, their larvae return to the ocean.