tridacna

from WordNet (r) 3.0 (2006)

Tridacna
    n 1: type genus of the family Tridacnidae: giant clams [syn:
         {Tridacna}, {genus Tridacna}]

from The Collaborative International Dictionary of English v.0.48

Tridacna \Tri*dac"na\, n. [L., pl., a kind of oysters, fr. Gr. ?
   eaten at three bites, ? tri- + ? to bite.] (Zool.)
   A genus of very large marine bivalve shells found on the
   coral reefs of the Indian and Pacific Oceans. One species
   ({Tridacna gigas}) often weighs four or five hundred pounds,
   and is sometimes used for baptismal fonts. Called also {paw
   shell}, and {fountain shell}.
   [1913 Webster] Tridactyl