muszle

Muszle is the Polish noun for shells, the hard outer coverings produced by many mollusks. In zoological terms, shells are protective exoskeletons composed primarily of calcium carbonate, secreted by the mantle. Most shells are layered, with an organic outer layer called the periostracum, a thick calcium carbonate layer (the ostracum), and, in many species, an iridescent inner layer known as nacre or mother of pearl.

Shells grow as the animal adds material at the edges; growth lines reveal age; colors and patterns arise from pigments in the shell. The shape and sculpture of shells reflect species, habitat, and life habits.

Two major architectural groups are univalves, with a single usually coiled shell (gastropods), and bivalves, with two hinged shells (clams, oysters, mussels). Cephalopods such as the nautilus retain external shells, while many other cephalopods have internal shells or none.

Habitats include marine, freshwater, and some terrestrial environments. Shells persist after the animal dies and are common in the fossil record, helping scientists study past biodiversity and climate.

Humans have long valued shells for ornament, tools, currency, and as raw material for beads and carved objects. In some species, shells also harbor pearls, formed when a foreign irritant becomes coated with nacre.