351.

Underwood’s Water Mouse

Rheomys underwoodi

French: Ichthyomys d'Underwood / German: Underwood-Wassermaus / Spanish: Raton de agua de Underwood

Other common names: Underwood's Ichthyomyine

Taxonomy. Rheomys underwoodi Thomas, 1906, Tres Rios, Cartago, Costa Rica.

Rheomys underwoodis the type species of the genus. Rheomys underwoodi and R. mexicanus appear to be closely related taxa and might be locally differentiated populations of a single species. Monotypic.

Distribution. Highlands of C Costa Rica and W Panama.

Descriptive notes. Head-body 130-142 mm, tail 148-158 mm, ear 4-7 mm, hindfoot 36-38 mm. No specific data are available for body weight. Underwood's Water Mouse is morphologically close to the Mexican Water Mouse ( R. mexicanus); both are large-bodied forms, with very large and broad hindfeet and tails conspicuously longer than head-body lengths. Tail of Underwood’s Water Mouse is bicolored, dark brownish or blackish above and dirty silvery below; while it is pure white below in the Mexican Water Mouse. Ears are always very small and buried in fur of head. Naked philtrum are absent.

Habitat. In and along clear, rocky-bottomed streams bordered by cloud forest vegetation at elevations of 1500-2000 m.

Food and Feeding. Underwood’s Water Mouse eats aquatic invertebrates, larvae of stoneflies, caddisflies, and mayflies.

Breeding. No information.

Activity patterns. Underwood’s Water Mouse is semi-aquatic and active day and night.

Movements, Home range and Social organization. Captive Underwood’s Water Mouse have been reported to swin with only its head and tip oftail above the water.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Underwood’s Water Mouse presumably has a large overall population, occurs in protected areas, and is unlikely declining at nearly the rate required to qualify for listing in a threatened category.

Bibliography. Hooper (1968b), Reid & Woodman (2008b), Starrett & Fisler (1970), Thomas (1906c¢), Voss (1988).