sea louse

from WordNet (r) 3.0 (2006)

sea louse
    n 1: marine isopod crustacean [syn: {sea louse}, {sea slater}]

from The Collaborative International Dictionary of English v.0.48

Sea louse \Sea" louse`\ (Zool.)
   Any one of numerous species of isopod crustaceans of
   {Cymothoa}, {Livoneca}, and allied genera, mostly parasites
   on fishes.
   [1913 Webster]