they are of the same family, both have a circular mouth with rasping teeth all around it.
the lamprey has a dark coloured skin and travels up rivers. the didnt know they were in the tees until large circular marks were found etched into the metal fish ladder where they clung on to travel up river. they latch on to the sides of fish like salmon and eat chunks off them.
the hagfish is almost skinless pink and blind. years ago it was regarded as a deep water fish where it would enter any orifice of a dead fish or fish trapped in a net and devour it from the inside.