The antonyms for Soft-shelled include Hard-shelled, Rigid, Tough, Crusty, Brittle, Stiff, and Firm. These terms vividly describe the opposite characteristics of soft-shelled, which represents an easily compressible or delicate substance, material or organism. For instance, hard-shelled refers to something that is tough, inflexible, and resistant to pressure or damage. Rigid also refers to a hard, unyielding, and stiff object or entity that cannot be easily altered or modified. Similarly, crusty suggests something that is dry, rough, and hard, like a baked crust, stale bread, or a thick layer of mud or dust. Overall, these antonyms highlight the diversity of characteristics that exist in the natural world and human-made artifacts.