Deskripsieng
Descriptive notes. Head — body 195 - 390 mm, tail 200 - 325 mm, ear 13 - 20 mm, hindfoot 46 - 80 mm; weight 210 - 1280 g. Data for one population in New South Wales found males to average slightly longer (head-body 310 mm vs. 290 mm) and slightly heavier (755 vs. 606 g) than females, but with no difference in average tail length. Populations in southern and eastern Australia are uniformly large-bodied and those from montane localities in New Guinea uniformly much smaller. There is more interregional variation in body size and proportions across northern Australian and in lowland Melanesia. The Common Water Ratis a heavily built, short-limbed semi-amphibious murine with dense, woolly pelt, heavily modified, flipperlike hindfeet, thick and well-furred tail, and small eyes and ears. Its degree of specialization for aquatic life makesit one of the most highly specialized Australo-Papuan murines, and one of the few species well known among members of the Australian public. Fur on upperparts is extremely dense and soft, typically grayish brown or brown overall, usually flecked with black, and often darker along middle of back than on flanks. Pelage has two distinct components — an outerlayer with body hairs measuring 12 - 14 mm in length, overtipped byslightly longer guard hairs, and a woolly inner layer measuring 8 - 9 mm; inner hairs are usually gray or brownish gray, outer hairs are yellowish at base and with brown tips, and guard hairs are uniform black. Fur on underparts is similarly dense, but both components shorter and paler, woolly inner layer to 5 - 6 mm and external layer to 9 - 10 mm; color of underparts more variable than that of upperparts, ranging from dusky gray to dull grayish white and ocherous yellow; texture and color of underparts extend to inner surfaces of limbs and throat but not to sides of head, which are dark. Boundary between flank and belly colorations is relatively abrupt. Woolly underfur tends to be more visible on limbs and sides of head, especially on vibrissal pads. Head is broad and somewhat flattened. Eyes fairly small and positioned near top of flattened head. Ears are somewhat thickened and with rounded margin, always projecting well beyond fur; skin on ears variably pigmented or pale, and usually hairy both inside and outside. Vibrissal pads and upperlips moderately inflated, contributing to swollen appearance of snout. Vibrissae are relatively numerous and suff, mostly unpigmented, and extending to ears or to rear of head. Front feet are small, with pigmented skin, and short hairs that are dark on wrist and usually paler on fingers; palmar pads broad and almost united; small nail on first digit and short but strong claws on remaining four digits. Hindfeet are elongate and very broad, upper surface with dark skin and hairs, all digits with short, strong claws; skin of plantar surface thickened and plantar pads have roughened, granular texture; interdigital pads distinct but closely adpressed; hallucal pad on inside of sole is elongate; all digits are united by folded skin to level of terminal pads, with distinct webbing present between second, third, and fourth digits. Tail is relatively long, but usually slightly shorter than head-body length, rounded in cross-section and muscular for most of length; scales flattened, typically in 13 - 14 rows / cm, and barely visible through dense cover of dark hairs that each subtend 6 - 7 scale rows and form short terminal tuft; hairs of basal portion of tail are dark brown to black, often darker than those on body; all but a few individuals have cream or white tail tip that accounts for between 5 % and 50 % oftotal tail length. Cranium hasflattened braincase, broad interorbital region, rostrum moderately broad and with heavy incisors, auditory bullae moderately large; molars quite large but reduced to two perquadrat, crowns with “ basined ” cusp arrangement. Mammae two on each side, both inguinal. Karyotype with 2 n = 28, including 21 pairs of telocentric autosomes in a graded series, and two small metacentric pairs; identical autosomal complements are recorded in species of Pseudomys, Mesembriomys, and Leggadina, and in some Melomys species, and this is interpreted as an ancestral arrangementfor Australian Hydromyini. X chromosome is a large acrocentric and Y chromosome is a tiny telocentric. Spermatozoa with moderately long tail (108 pm), and relatively short (7 pm) sperm head that is broad basally, with narrow apical hook and two accessory ventral hooks. Glans penis has bulbousdistal portion, large dorsal papilla, outer crater rim that is weakly papillate, low inner crater, and robust baculum with broad, weakly notched base.
Sumber: Muridae
