Hardshells

Hardshells are an informal term for animals that possess a rigid external covering that protects soft tissues. The term is commonly applied to crustaceans such as crabs, lobsters, and shrimp, as well as mollusks with shells. Hardshells are characterized by a protective, often calcified, outer layer.

In crustaceans, the exoskeleton is primarily chitin strengthened with calcium carbonate in many species. The shell or carapace is periodically molted and renewed. In mollusks, the external shell is secreted by the mantle and composed largely of calcium carbonate, with nacre sometimes present inside.

Growth requires molting (ecdysis). Animals shed the old shell and synthesize a larger one. The molt period leaves the animal vulnerable until the new shell hardens. Molting frequency varies, with juveniles typically molting more often than adults.

Hardshells occupy diverse habitats from oceans to freshwater and, among crustaceans, some land-dwellers. Diet ranges from detritus to predation. Reproduction varies; many have complex life cycles with free-swimming larvae such as nauplius or zoea stages in crustaceans.

Humans depend on hardshell crustaceans for seafood; the hard shells complicate processing but contribute to texture and protection. Conservation concerns include overharvesting, habitat degradation, and climate effects on calcification. Some fisheries regulate harvest or size to protect breeding individuals.

Diversity includes crustaceans (crabs, lobsters, shrimp, barnacles) and mollusks (bivalves, snails). Both groups show a wide array of shell shapes, sizes, and adaptations to protect against predators and environmental conditions.