Skalsystemet

Skalsystemet is a term used in Norwegian biology to refer to the organization and development of the protective outer covering—the shell or exoskeleton—of certain invertebrates, chiefly mollusks and arthropods. The concept encompasses the structural layers, formation processes, and functional roles of shells. In mollusks, shells typically consist of layers laid down by the mantle, including an organic periostracum and mineral layers such as the prismatic layer and nacre. Shell growth occurs at the margin as the mantle secretes new material, and pigmentation can add color patterns. In arthropods, the exoskeleton is formed largely of chitin and proteins, with layered organization that provides rigidity, protection, and muscle attachment sites; molting is a key part of growth.

The skalsystemet has significance in taxonomy and paleontology because shell morphology and growth patterns provide diagnostic characters and insights into evolutionary relationships. It also informs biomineralization research, materials science, and paleoclimate studies through shell chemistry and structure.

In Norwegian scientific usage, the term may be used across disciplines to describe the general principle of external protective coverings, though field-specific terminology varies. See also biomineralization, molluscan shell anatomy, exoskeleton.