Source : Webster's Revised Unabridged Dictionary (1913)

Cercaria \Cer*ca"ri*a\, n.; pl. {Cercarle} [NL., fr. Gr. ?
   tail.] (Zo["o]l.)
   The larval form of a trematode worm having the shape of a
   tadpole, with its body terminated by a tail-like appendage.

Source : WordNet®

cercaria
     n : tadpole-shaped parasitic larva of a trematode worm; tail
         disappears in adult stage
     [also: {cercariiae} (pl), {cercariae} (pl)]