The marine otter (Lontra felina) is a rare and relatively unknown South American mammal of the weasel family (Mustelidae).

[5][6] Its fur is coarse, with guard hairs measuring up to 2 cm (0.79 in) in length covering dense, insulating underfur.

[citation needed] The marine otter mainly inhabits rocky shorelines with abundant seaweed and kelp, and infrequently visits estuaries and freshwater rivers.

It appears to select habitats with surprisingly high exposure to strong swells and winds, unlike many other otters, which prefer calmer waters.

Caves and crevices in the rocky shorelines may provide them with the cover they need, and often a holt will have no land access at high tide.

Rocky intertidal zones with natural crevices are ideal for marine otter dens and feeding areas.

[7] Though generally avoidant of humans, their inhabitance of fishing villages is an indicator of the marine otter's ability to adapt to urbanization.

Studies have shown latitudinal variations in diet, feeding periods, and dive time throughout the marine otter's distribution.

[9] The otters on Isla La Vieja, Peru presumably prey on a colony of Peruvian diving petrels regularly.

[10] The species shows opportunistic feeding behavior, sometimes eating small mammals and even fruit of plants like Greigia sphacelata and Fascicularia bicolor.

A phylogenetic study by C. G. Van Zyll De Jong in 1987 proposed the following phenogram of the lutrinae, based on morphological data.