The jawless mouth of a lamprey attaches to prey using suction.
“The lamprey uses a sucker-like jawless mouth to cling to the trout, and has a vicious abrasive tongue with which to gorge a hole in its host’s body. There it laps up the body fluids oozing from the wound.” (Foy and Oxford Scientific Films 1982:50)
Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.