Cyclostomes have an elongated body bearing 6-15 pairs of gill slits for respiration, so (a) matches with (ii) in column-II. Air bladder is present in bony fishes belonging to class Osteichthyes which regulates buoyancy, so (c) matches with (iv) in column-II. Trygon, a cartilaginous fish, possesses poison sting, so, (d) matches with (i) in column-II. Heterocercal caudal fin is present in members of class Chondrichthyes, so (b) matches with (iii) in column-I.