Mouth is ventral, suctorial and circular (the tongue is with denticles) hence, the class is called Cyclostomata (Gk, cyklos-circular; stoma-mouth). They have a sucking and circular mouth without jaws. All living members of Cyclostomes are ectoparasite on some fishes. 5-16 pairs of gills are present in lateral sac-like pouches of pharynx, while gill-slits are 1-16 pairs. The male salamanders (genus Ambystoma) are a group that are endemic to North America.