Sea otters are the largest member of the family Mustelidae. Males weigh 22 to 45 kg and are 1.2 to 1.5 m in length. Females are slightly smaller, weighing 14 to 33 kg and measuring 1 to 1.4 m in length. The tail comprises less than a third of the body length. The pelage is brown or reddish brown. Sea otter fur is the densest of all mammals, with about 100,000 hairs per square centimeter. Since sea otters do not have any insulating fat, the fur is responsible for maintaining warmth. The hind legs are long and the paws are broad, flat, and webbed. The forelimbs are short and have retractable claws. Sea otters are the only carnivorans with just 4 lower incisors. Females have two mammae.

(Estes 1980; Nowak 1999)

Range mass: 14 to 45 kg.

Range length: 1 to 1.5 m.

Other Physical Features: endothermic ; bilateral symmetry

Average basal metabolic rate: 98.479 W.