mantis shrimp

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various burrowing predatory marine crustaceans of the order Stomatopoda, chiefly of tropical waters, having stalked eyes and a pair of knifelike claws that resemble the legs of a praying mantis and are used for striking or spearing prey.

from The Century Dictionary.

• noun A stomatopodous crustacean of the family Squillidæ, as Squilla mantis or S. empusa: so called from the resemblance to the insect called mantis. See Gonodactylus, Squilla. Also called mantis-crab and locust-shrimp.
• noun A læmodipodous crustacean of the family Caprellidæ, as Caprella linearis; a specter-shrimp: so called for the same reason as above.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun tropical marine burrowing crustaceans with large grasping appendages