Petromyzon (Lamprey)

Petromyzon is a member of class cyclostomata commonly known as lamprey. lamprey are both marine and fresh water forms. They are usually used for laboratory studies because of their large size.
It is world wide in distribution and found in both salt and fresh water.
Its life cycle includes two different phases. The larval phase, called Ammocoete is a fresh water, sedentary, filter feeding and microphagus creature. The fish like adult lives in the sea and is parasite on fishes.
They destroy valuable fish by feeding on their blood and body fluids. The scars left on the body of fishes render them unfit for the market.