The DICT Development Group

  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

  Clam \Clam\ (kl[a^]m), n. [Cf. Clamp, Clam, v. t.,
     Clammy.]
     1. (Zool.) A bivalve mollusk of many kinds, especially those
        that are edible; as, the long clam ({Mya arenaria), the
        quahog or round clam ({Venus mercenaria), the sea clam or
        hen clam ({Spisula solidissima), and other species of the
        United States. The name is said to have been given
        originally to the Tridacna gigas, a huge East Indian
        bivalve.
        [1913 Webster]
  
              You shall scarce find any bay or shallow shore, or
              cove of sand, where you may not take many clampes,
              or lobsters, or both, at your pleasure. --Capt. John
                                                    Smith (1616).
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              Clams, or clamps, is a shellfish not much unlike a
              cockle; it lieth under the sand.      --Wood (1634).
        [1913 Webster]
  
     2. (Ship Carp.) Strong pinchers or forceps.
        [1913 Webster]
  
     3. pl. (Mech.) A kind of vise, usually of wood.
        [1913 Webster]
  
     Blood clam. See under Blood.
        [1913 Webster]

  Tridacna gigas
      n 1: a large clam inhabiting reefs in the southern Pacific and
           weighing up to 500 pounds [syn: giant clam, Tridacna
           gigas]