Lampreys

Lampreys (sometimes also called lamprey eels) are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers (lambere: to lick, and petra: stone). While lampreys are well-known for those species which bore into the flesh of other fish to suck their blood, most species of lamprey are non-parasitic and never feed on other fish. In zoology, lampreys are sometimes not considered to be true fish because of their distinctive morphology and physiology.

Ref: en.wikipedia.org and looneynature.com