The Collaborative International Dictionary of English v.0.48:

Zoea \Zo"["e]*a\, n. [NL., fr. Gr. ? life.] (Zool.)
   A peculiar larval stage of certain decapod Crustacea,
   especially of crabs and certain Anomura. [Written also
   zoaea.]
   [1913 Webster]

   Note: In this stage the anterior part of the body is
         relatively large, and usually bears three or four long
         spines. The years are conspicuous, and the antennae and
         jaws are long, fringed organs used in swimming. The
         thoracic legs are undeveloped or rudimentary, the
         abdomen long, slender, and often without appendages.
         The zoea, after casting its shell, changes to a
         megalops.
         [1913 Webster]