Hardistiella Interrelationships of the Hyperoartia. The skin of lampreys is entirely naked ans slimy, and their seven gill openings extend behind the eyes. Whether marine or fresh water, lampreys always spaw and lay eggs in brooks and rivers. Anadromous lampreys, when adult, return to the sea, where they become mature, and live there for one or two years. Then they return to rivers, reproduce and generally die.
Many lampreys are parasites.
They attach on other fishes by means of their sucker, scrape their skin with their rasping tongue, and suck their blood. All lampreys, however can also feed on small invertebrates. The sucker is also for them a means to travel upstreams in rivers. Lampreys have an amphitropical distribution and are restricted to relatively cold waters. Geotria and Mordacia are the only lampreys of the southern hemisphere, all other genera live in the northern hemisphere.