Otter is the common name for any of the 13 species that make up the taxonomic subfamily Lutrinae, which is part of the family Mustelidae (weasels, otters & badgers).

Otters are carnivorous weasel-like mammals that survive, with two exceptions, in both freshwater and land environments. The exceptions are the Sea Otter, Enhydra lutris, which is a strictly marine habitat species, and the Marine Otter, Lontra felina, which lives in marine and estuarine environments.

Otters can be found in rivers, streams, lakes, marshes, estuaries, and marine coasts throughout the world. They always stay in close proximity to water, though they do sleep on land (the exception again being the sea otter). They mark their territories with anal scent glands, as do most members of the Mustelidae family.

Like weasels, otters have long, slender bodies and short legs. Their tales are thick and muscular, as they help otters to maneuver in water. Paws are webbed for swimming, and most species have claws.

All otters have a very think coat of fur which is comprised of a soft, dense undercoat and a course overcoat. The two layers of fur trap air between them, which serves to keep the otter warm while in the water. This is in contrast to seals, which have a layer of blubber to keep them warm.

Otters have a high metabolic rate and must eat a lot to maintain their body temperature in the cool water. River otters eat about 15% of their body weight each day, while sea otters must eat a whopping 25% of their body weight per day. Their main diet is fish, but they also eat crabs, frogs, crayfish and shellfish. Birds and small mammals are also occasionally on the menu.

Otters are notable for being among the fairly small list of animals that can use tools (others being apes, dolphins, elephants and several species of bird). Sea otters have been observed placing a rock on their chest while floating on their back to use for cracking open shellfish.

Most species of otter are threatened or endangered. They are particularly susceptible to environmental degradation. Pollution, loss of habitat, agricultural runoff, and hunting are some of the threats they face. Coastal oil spills are a particularly fatal menace, as the oil covers their fur, rendering it useless for protection from the cold.

Interestingly, there appears to be a special vocabulary related to otters. Following is a short glossary of terms as found in Wikipedia's Otter article:

male otter: dog-otter
female otter: bitch
baby otters: cubs
group of otters: romp
otter den: holt
otter dung: spraint or scat

On the subject of Lutrinae taxonomy, there are some differences among taxonomists in how Lutrinae are classified. In the past, American otters were classified as genus Lutra, but now they are often found in their own genus, Lontra, i.e., new world otters. Also, Spotted necked otters are sometimes classified in their own genus, Hydrictis, as in Hydrictis maculicollis. SeaPics.com photographers, depending on the source they use, may arrive at different Latin names. They may choose to categorize a Northern river otter, for example, as Lontra Canadensis or Lutra Canadensis.

© Lutrinae information assembled from published and on-line sources by Kevin Miler for SeaPics.com. Dec. 14, 2007.

Sources:

http://en.wikipedia.org/wiki/Lutrinae

http://www.lioncrusher.com/Lutrinae.htm

http://www.otterproject.org/site/pp.asp?c=8pIKIYMIG&b=277649

http://www.umich.edu/~esupdate/library/96.12/watson.html