Basic Otter Anatomy

A generalized overview of the internal and external anatomy of otters:

External Anatomy

* Otters range in size from 65 cm (Asian small clawed otter) to 180 cm (giant otter) long from nose to tail.

* Otter tails are long and strong. The sea otter has, comparatively, the shortest and least muscular tail of all of the otters.

* All species have long, flexible bodies designed for speed and agility, especially under water. River otters can run ~20 mph (likely faster in bursts) and giant otters can swim 9 mph.

* All otters, except sea otters, have anal scent glands at the base of the tail used for scent marking.

* Fur is very dense and usually very silky (composed of guard-hairs and fine under-hairs) and varies through shades of brown, frequently with lighter undersides and/or spots.

* Otters can close their ears and noses underwater.

* Otters have very good hearing.

* Noses are one of the distinguishing features between otter species, some even have hairy noses! Otters have a good olfactory sense (they have a good sense of smell!). They all have vibrissae (whiskers) that are so sensitive they can sense under water vibrations! (this is very helpful in detecting prey)

* Feet are generally webbed with claws. Otters' feet are distinctive and say a lot about where the species live. The soles of all otters' feet are hairless, except for the sea otter whose hind feet are furred.


Internal Anatomy

Internal Anatomy. L. Spelman 1994

* Otters hold their breath to dive for food, escape predators, and, likely, for fun! River otters can hold their breath 6-8 minutes. The longest sea otter dive recorded is 4 minutes 25 seconds (though they can likely hold their breaths a little longer).

* Otters have a higher rate of metabolism than most similarly sized mammals. Water conducts heat much faster than air, so they are constantly working to keep themselves warm. The super-dense fur just isn't enough to do it on its own, so they have to eat a lot!

* Otter's eyes have specialized lenses and corneas that correct their vision for the change in light refraction between air and water environments.

 
Some links to additional anatomical exams and necropsies:

* An interactive cryo-cross-section of a sea otter fetus.

* Step-by-step river otter dissection .

 * A comprehensive "pictorial guide" of sea otter anatomical exams and necropsies from US Fish and Wildlife Service, Region7, Alaska Veterinary Pathology Services, and Alaska Sea Life Center.