The Collaborative International Dictionary of English v.0.48:

Squilla \Squil"la\ (skw[i^]l"l[.a]), n.; pl. E. Squillas
   (-l[.a]z), L. Squillae (-l[=e]). [L., a sea onion, also, a
   prawn or shrimp. See Squill.] (Zool.)
   Any one of numerous stomapod crustaceans of the genus
   Squilla and allied genera. They make burrows in mud or
   beneath stones on the seashore. Called also mantis shrimp.
   See Illust. under Stomapoda.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mantis \Man"tis\, n. [NL., fr. Gr. ? a prophet.] (Zool.)
   Any one of numerous species of voracious orthopterous insects
   of the genus Mantis, and allied genera. They are predacious
   long-bodied large-eyed insects of warm regions, are
   remarkable for their slender grotesque forms, and for holding
   their stout anterior legs in a manner suggesting hands folded
   in prayer. The common American species is Mantis Carolina.
   [1913 Webster]

   Mantis shrimp. (Zool.) The Squilla, a tropical marine
      burrowing crustacean with large grasping appendages. Also
      called mantis crab and mantis prawn.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mantis shrimp
    n 1: tropical marine burrowing crustaceans with large grasping
         appendages [syn: mantis shrimp, mantis crab]