Otters are aquatic mammals whose physical form is highly adapted for a life spent largely in or near water. Their specialized body plan allows them to move with fluid grace, whether navigating river currents or floating in the ocean. The otter’s streamlined silhouette and thick, waterproof coat all contribute to its success as a semi-aquatic predator.
General Shape and Size
The otter’s overall appearance is defined by a long, serpentine body that is perfectly streamlined for swimming. This elongated shape tapers smoothly from the head to the tail, minimizing drag in the water and creating a torpedo-like profile. Most species possess a thick, muscular neck that appears to merge seamlessly with the shoulders, further enhancing the animal’s hydrodynamic form.
Otters are typically low to the ground, given their relatively short limbs, which contributes to their characteristic undulating gait when moving on land. The size range is quite broad across the 14 different species, with total lengths spanning from about 2 to nearly 6 feet (0.6 to 1.8 meters). Weights can vary significantly, starting from the smallest, the Asian small-clawed otter, at around 7 pounds (3.5 kilograms), up to the heaviest sea otters, which can exceed 90 pounds (41 kilograms).
The Insulating Coat and Facial Features
The otter’s defining visual element is its incredibly dense, double-layered coat. The outer layer consists of long, coarse guard hairs that lie flat and are somewhat water-repellent, protecting the softer underfur beneath. The extremely thick underfur traps a layer of air against the skin, providing insulation and buoyancy to keep the animal warm in cold water.
This fur typically ranges in color from various shades of brown, often appearing sleek and wet when the animal emerges from the water. The fur on the underside, or ventral surface, is noticeably lighter, often a silvery or tan shade, providing countershading. The head of an otter is relatively small and flattened, situated on the thick neck.
Its eyes are small and set high on the head, an adaptation that allows the animal to keep a lookout while most of its body remains submerged. The ears are also small and possess the ability to close off when the otter dives underwater. The muzzle is framed by prominent, long, stiff whiskers, known as vibrissae. These specialized sensory hairs are used to detect subtle movements and vibrations in murky water, helping the otter locate prey.
Specialized Aquatic Appendages
The otter’s limbs are short and robust, built for powerful movements both on land and in the water. The paws are adapted for aquatic life, appearing broad and somewhat flat. In most species, the five toes on each paw are connected by webbing, which creates a larger surface area for propulsion when swimming.
The extent of this webbing can vary between species, with some clawless otters having only partial webbing. Most otters possess short, non-retractable claws on their feet, which are used for traction on land and grasping prey. The tail is a strong, muscular feature that is thickest at the base and then visibly tapers to a point. This structure acts as a powerful rudder and stabilizer, generating much of the force needed to propel the otter through the water.