Lamprey -
a. 7 pairs of gill slits are present.
b. 10 pairs of cranial nerves are present.
c. Brain is better developed.
d. It exhibits indirect development.
e. Unisexual
f. Two semi-circular canals are present.
h. Habitat - marine as well as fresh water

Hag fish -
a. 6-15 pairs of gill slits are present.
b. 8 pairs of cranial nerves are present.
c. Brain is poorly developed.
d. It exhibits direct development.
e. Hermaphrodite
f. One semi-circular canal is present.
h. Habitat - Exclusively marine