Silmlaste sugukonda arvatakse kolm alamsugukonda: Geotriinae, Mordaciinae ja Petromyzontinae. Neist kaks esimest esindavad silmlasi, kes elavad lõunapoolkeral (kokku 4 liiki), kolmandasse kuuluvad silmlased elavad aga põhjapoolkeral.
Lampreys are aquatic, jawless vertebrates belonging to the Order Petromyzontiformes. The order comprises 39species widely distributed in the Northern and Southern hemispheres, but virtually absent in the intervening tropicalzone. There is one family in the Northern Hemisphere (Petromyzontidae) comprising 35 species and two families inthe Southern Hemisphere (Geotriidae and Mordaciidae) comprising, respectively, one and three species.
