soft-shell

from The Collaborative International Dictionary of English v.0.48

Soft-shell \Soft"-shell`\, Soft-shelled \Soft"-shelled`\, a.
   Having a soft or fragile shell.
   [1913 Webster]

   {Soft-shell clam} (Zool.), the long clam. See {Mya}.

   {Soft-shelled crab}. (Zool.) See the Note under {Crab}, 1.

   {Soft-shelled turtle}. (Zool.) Same as {Soft tortoise}, under
      {Soft}.
      [1913 Webster]