Hair and Fur

Abstract

This chapter discusses the structure and function of hair and fur in sea mammals. The presence of hair is one of the characteristics that distinguish mammals from other vertebrates. Hair consists of keratinized epidermal cells, formed in hair follicles located in the dermal layer of the skin. Adaptations to an aquatic or amphibious lifestyle are apparent in marine mammal skin and hair. Pinniped and sea otter ( Enhydra lutris ) hairs are flattened in cross-section rather than round as in other carnivores. This is evidently an adaptation for enhancing streamlining of the body and reducing drag during swimming. Pinnipeds and sea otters have diffuse smooth muscle in their dermis, but they lack true arrector pili muscles. Pinnipeds, sea otters, and polar bears ( Ursus maritimus ) possess sebaceous glands and sweat glands, but these are absent in cetaceans and sirenians. Cetacean skin is hairless except for a few vibrissae or bristles occurring mostly on the rostrum or around the mouth. These are usually lost before or soon after birth. Sirenians have widely scattered hairs. The integument of pinnipeds, sea otters, and polar bears generally has two layers of hair. The outer protective layer consists of long, coarse guard hairs and the inner layer is composed of softer intermediate hairs or underfur. Polar bear, sea otter, and otarid guard hairs are medullated (having a sheath), whereas phocid and walrus hairs ( Odobenus rosmarus ) are not. The hairs typically grow in groups or clumps, with a single guard hair emerging cranial to one or more underfur hairs.