The skin and its derivatives (hair, nails, feathers, horns, antlers, and glands), which in multicellular animals protect against invading foreign microorganisms and prevent the loss or exchange of internal þuids. PICTURE
In zootomy, the integumentary system is often the largest organ system of an animal by surface area, comprising skin, hair, feathers, scales, nails, sweat glands and their products (sweat and mucus). It distinguishes, separates, protects and informs the animal with regard to its surroundings. Small-bodied invertebrates of aquatic or continually moist habitats respire at their outer layer (integument).