Question

Agnatha or cyclostomata are characterized by
A. Absence of jaws and presence of sectoral mouth
B. Presence of sectoral mouth, and absence of jaws, the presence of of single nostril in the unpaired fins
C. Absence of mouth, presence of single nostril
D. Round mouth with triradiate lips

Answer 1

Hint: In the jawless fish cyclostomata is a paraphyletic super class present in it. It includes the class of agnatha and an extinct class of the ostracoderm. In the jawless fish they have a single median nostril, and mouth present in the form of sectorial and circular, no paired appendages or fins are present in the elongated body.

Complete answer:
Cyclostomata are the primitive vertebrates that present in jawless form in the fresh and marine water. It showed a compressed tail and eel-like body. In the cyclostomata unpaired fins are present and supported by the cartilaginous fin rays by the endian fin. The scale has less slimy, soft and smooth skin present in it. In the tail protector and trunk Z shaped myomeres present in it that help to the movement of the tongue and muscles.
In the group of agnatha seen as a true coelom but vertebrates will not have jaws present in it. The mouth is circular in shape and works as a sucker and surrounded by tentacles. Stomach is absent and tongue beers teeth, or esophagus leads into the intestine. Notochord is absent throughout life but the skull is simple and primitively present inside it.

Therefore the correct option is (B).

Note: The round body, elongated like an eel, present unpaired fins, median fins that attached with the cartilaginous fin rays, soft and smooth skin, absence of the spleen and exoskeleton, presence of the notochord are the main characteristics found in the cyclostomata. Cyclostomata is a superclass of the cyclostomata and subphylum of the vertebrata.