Which of the following does not come under the Class Mammals?

Lamprey (or Petromyzon) belongs to class cyclostomata. The lamprey has about (1 \mathrm{~m}). long greenish brown, cylindrical body with smooth, scaleless, slimy skin; anterior circular, jawless mouth; a single dorsal naris; seven pairs of circular gill slits; 2 dorsal fins and a tail fin. Its life cycle includes two quite different phases. The larval phase (called ammocoete) is a fresh water sedentary, filter feeding and microphagus creature reminiscent of the lancet. The fish like adult lives in the sea and is parasitic on fishes.