The salient features of class Cyclostomata are :
(a) They are living fossils of once abundant jawless fishes.
(b) They have long, eel like body with compressed tail.
(c) The skin is soft, smooth, shiny and is without scales.
(d) Paired fins, and associated girdles are absent but median fins are present.
(e) The exoskeleton is cartilaginous. Notochord persists throughout life.
(f) The mouth is jawless, circular and suctorial with a tongue bearing horny teeth.
(g) The heart is two chambered-one auricle and one ventricle.
(h) There is single medium olfactory sac. Ear consists only of membranous labyrinth.
(i) The body temperature is variable.