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 ?
B. Petromyzon sp.
The given characteristics belong to the class Cyclostomata. Members of this class are ectoparasites on some fishes. They have an elongated body bearing 6-15 pairs of gill slits for respiration. Cyclostomes have a sucking and circular mouth without jaws. Their body is devoid of scales and paired fins. Cranium and vertebral column are cartilaginous. Petromyzon (Lamprey) and Myxine (Hagfish) are examples of class Cyclostomata. Scoliodon belongs to class Chondrichthyes. Exocoetus belongs to class Osteichthyes. Branchiostoma belongs to subphylum Cephalochordata. Thus, Petromyzon sp. fits best with the given characters. Answer: Petromyzon sp.
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