1. Cyclostomata means - circular mouth without jaw
2.6 -15 pairs gills present
3.Head and brain poorly developed ,body devoid of scales and paired and fins
4. Cranium and vertebral column are cartilaginous
5. Closed blood circulation type present
6.All living members are ectoparasites on some fishes
7. All are marine but during reproduceing and fertilisatilng time they move fresh water
8. After spawing ,within a few days they die
9. Their larvae, after metamorphosis, return to ocean
Ex- lamprey ( petromyzon), Hagfish
