Parasitic lampreys
These parasitic sea lampreys attach to their lake trout host by suction and use their rough tongues to rasp away flesh in order to feed on the trout's blood.
Source
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"OpenStax College, Fishes. October 17, 2013."
http://cnx.org/content/m44687/latest/Figure_29_02_02.jpg
OpenStax CNX
CC BY 3.0.
