Lamprey

noun

an eel-like aquatic jawless vertebrate that has a sucker mouth with horny teeth and a rasping tongue. The adult is often parasitic, attaching itself to other fish and sucking their blood.

Middle English: from Old French lampreie, from medieval Latin lampreda, probably from Latin lambere ‘to lick’ + petra ‘stone’ (because the lamprey attaches itself to stones by its mouth).