238.

Husson’s Water Rat

Hydromys hussoni

French: Hydromys de Husson / German: Husson-Schwimmratte / Spanish: Rata de agua de Husson

Other common names: Husson's Hydromys, Western Hydromys, Western Water Rat

Taxonomy. Hydromys hussoni Musser & Pik, 1982,

“Enaratoli (3°55°40”S, 136°22°6”E), 1765 m, on the east side of Paniai Lake [formerly Wissel Lakes],” Papua Province, Indonesia .

The specimen that A. C. Ziegler reported in 1984 as a Papua New Guinean occurrence of H. hussoni was later used by K. M. Helgen to describe a new species, H. ziegleri . Ziegler’s attribution was repeated by G. G. Musser and M. D. Carleton in 1993 and 2005, and by T. F. Flannery in 1995. Monotypic.

Distribution. Known only from the catchment of Paniai Lake, W New Guinea, at elevations of 1750-1765 m.

Descriptive notes. Head-body 128-167 mm, tail 103-152 mm, ear 11-14 mm, hindfoot 25-31 mm. No specific data are available for body weight. Hydromys species are plump, shortlimbed, semi-amphibious murines with hindfeet that are moderately long and broad and have partially webbed toes. Husson’s Water Rat is the second smallest member of genus. Fur on upperparts is short and dense. Overall fur color is dark chestnut, richer in tone along mid-back but with buffy or ocherous hues on flanks and sides of head. Underparts and insides of limbs are dark gray, tinged with buff, or rich ocherous and lightly suffused with gray, the same tones extending to chin, throat, and cheeks. Boundary between flank and belly colorationsis diffuse. Rump often has small clumps of white hairs, producing diffuse spots. Head is broad and somewhatflattened, with no obvious neck. Vibrissal pads dark; vibrissae numerous but fine, reaching to ear. Eyes are moderately reduced, and ears small, dark, and thinly furred. Forefeet are brown above onto digits, with nail on first digit and unpigmented claws,all strongly curved and sharp, on other digits. Hindfeet are elongate and broad, upper surface tan or brown but paler than forefeet, all digits bearing unpigmented claws, strongly curved and sharp, second to fourth digits united by band of conspicuous webbing. Tail (averages 85% of head-body length), rounded in cross-section but not conspicuously thickened, has skin dark brown above and below and is densely furred to tip, with individual hairs extending for length of many scale rows; tail fur is dark brown to tip in 20% of individuals, but in majority it terminates in white section measuring 2-19% oftail length; tail terminates in short tuft. Cranium is of typical murine proportions, but interorbital region is broad and dorsal profile isflattened. Incisors have pale yellow enamel, deeper hue in upper than in lower pair; molars reduced to two per quadrat, crowns with “basined” cusp arrangement typical of Hydromys . Mammae two on each side, both inguinal.

Habitat. Type series of Husson’s Water Rat is not accompanied by any information on habitat. All specimens, however, were obtained in vicinity of Paniai Lake or on streams flowing into the lake, and it is likely that this species is closely associated with this regionally unique cluster of waterbodies. Even in late 1930s, when the area was first brought under colonial influence, the area around the lakes was densely settled, with large areas devoted to subsistence gardening. Aquatic fauna of the lakes is limited, with only a few small-bodied native fishes and a variety of crustaceans.

Food and Feeding. No information.

Breeding. No information.

Activity patterns. No information.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Data Deficient on The IUCN Red List. The Paniai Lakes and feeder streams may represent the entire available habitat for this species. These waterbodies occupy a tectonic depression between the Weyland and Sudirman Ranges of Central Cordillera of New Guinea, and represent a regionally unique landform in the western part of New Guinea. Similar waterbodies farther east in New Guinea support populations of the Earless New Guinea Water Rat ( Crossomys moncktoni), which may have an overlapping ecological niche, although latter species is well adapted also for life in montane torrents, as well as lakes. The lakes are contained within the Enaratoli Nature Reserve, but there has been no follow-up survey of them since type series was collected, in 1939. Human population of Enaratoli has increased significantly since 1963, when Indonesian administration of Papua Province commenced, but impact of this on the ecology of the lakes and surrounding habitats is undocumented.

Bibliography. Flannery (1995b), Helgen (2005), Leary, Singadan, Menzies, Helgen, Allison et al. (2008b), Musser & Carleton (1993, 2005), Musser & Piik (1982), Ziegler (1984).