Agnatha is represented by which among the following class ?

Cyclostomata

The correct answer is Option (1) -Cyclostomata

All living members of the class Cyclostomata 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.

Circulation is of closed type. Cyclostomes are marine but migrate for spawning to fresh water. After spawning, within a few days, they die.

Their larvae, after metamorphosis, return to the ocean. Examples: Petromyzon (Lamprey) and Myxine (Hagfish). 

General Characters of Gnathostomata:

1. Two well-formed jaws encircle the mouth aperture in all members of this group.

2. Paired and in some cases jointed appendages are present in Gnathostomata.