Soft-shell \Soft"-shell`\, Soft-shelled \Soft"-shelled`\, a. Having a soft or fragile shell.

Soft-shell clam (Zo["o]l.), the long clam. See Mya.

Soft-shelled crab. (Zo["o]l.) See the Note under Crab, 1.

Soft-shelled turtle. (Zo["o]l.) Same as Soft tortoise, under Soft.

Source: Webster's Revised Unabridged Dictionary (1913)