The Collaborative International Dictionary of English v.0.48:

Sea slater \Sea" slat"er\ (Zool.)
   Any isopod crustacean of the genus Ligia.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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