Beetles, lotus leaves and your fingernails all have a 'cuticle'
'Cuticle' names a tough, flexible, non-mineral outer layer, and nature has invented it many times over. The skin fold at the base of a fingernail, the armour of an insect, the waxy sheen on a leaf and the peelable skin of a mushroom cap all share the name, yet they differ in origin, chemistry and job.
In people, the word usually refers to the thickened skin around finger- and toenails, properly called the eponychium, or to the outer layer of overlapping dead cells on each hair shaft that anchors the hair in its follicle. It is sometimes used loosely for the epidermis itself. These structures are not related to the cuticles of other organisms; biologists describe the various types as non-homologous.
Among invertebrates, a multilayered cuticle outside the skin forms an exoskeleton, especially in arthropods and roundworms. Roundworm cuticles are built largely from cross-linked collagens and insoluble proteins called cuticlins. Arthropod cuticles rely on chitin, a sugar-based polymer bonded to proteins, and their stiffness depends on which proteins are present and how much chitin there is. Tiny nanostructures in insect cuticles can create colour without pigment, and in the mealworm beetle darker individuals appear to resist disease better than tan ones.
Plants coat their leaves, young shoots and other above-ground parts in a waxy cuticle made of the polymers cutin or cutan soaked with wax. It keeps water in and pathogens out, and keeps surfaces from getting soaked. Desert plants such as cacti grow very thick ones, as do plants exposed to salty sea spray. The sacred lotus goes further: its surface is sculpted into microscopic raised bumps so closely spaced that water cannot seep between them, so droplets touch only a fraction of the leaf and roll away. The marble berry, Pollia condensata, uses its cuticle for dazzling structural colour.
Mushrooms have one too. The skin removed when peeling a mushroom cap is often called its cuticle, though mycologists may prefer pileipellis, Latin for the skin of a cap. It is distinct from the fleshy interior and from the spore-bearing layer beneath.
Source: Cuticle
