Cuticles

A cuticle /ˈkjuːtɪkəl/, or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homologous, differing in their origin, structure, function, and chemical composition.

In human anatomy, cuticle (sometimes confused with eponychium) refers to several structures. It refers to the layers of epidermal cells or keratinocytes that produce the horn protein keratin, and also to the superficial layer of overlapping cells covering the hair shaft (cuticula pili) that locks the hair into its follicle (See also Cuticle (hair)).

In zoology, the invertebrate cuticle or cuticula is a multi-layered structure outside the epidermis of many invertebrates, notably roundworms and arthropods, in which it forms an exoskeleton (see arthropod exoskeleton).

The main structural components of the nematode cuticle are proteins, highly cross-linked collagens and specialised insoluble proteins known as "cuticlins", together with glycoproteins and lipids.

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