The Collaborative International Dictionary of English v.0.48:

Sea crawfish \Sea" craw"fish`\ Sea crayfish \Sea" cray"fish`\
   (Zool.)
   Any crustacean of the genus Palinurus and allied genera, as
   the European spiny lobster (Palinurus vulgaris), which is
   much used as an article of food. See Lobster.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sea crawfish
    n 1: large edible marine crustacean having a spiny carapace but
         lacking the large pincers of true lobsters [syn: spiny
         lobster, langouste, rock lobster, crawfish,
         crayfish, sea crawfish]