Humid Andean forests of South America.

Biogeographic Regions: neotropical (Native )

Caluromysiops irrupta has a head and body length of 25-30 cm and tail length of 31-33 cm. Its most distinguishing features are the two separate, black lines on the upper part of the body. These black lines begin on the forefeet and run onto the back, join on the shoulders, then separate again and run parallel to each other down the back and over the rump to the hind limbs. There are also faint lines that run through the eyes and along the middle of the belly with the underpart grayish in color (Walker 1975). The tail of Caluromysiops has dense, long and woolly fur, but the underside of the last three-fourths of the tail is naked. Also, the basal three-quarters of the tail on the upper side has a darker shade of gray than the body, and the last quarter of the tail is creamy white. The tail has 30-31 vertebrae and is prehensile, allowing the animal to use it for clinging to branches with the tail while reaching for food. In addition, the hind limbs of Caluromysiops are relatively shorter than the forelimbs (Izor and Pine 1987).

The skull of Caluromysiops also has some distinct features. The eyes are large and protruding (a characteristic of tree-dwellers), the sagittal crest is pronounced in adults, the zygomatic arches are robust, the rostrum is short, the mandible is deep and the molars are relatively larger (a distinctive feature in Calurymysiops). The dental formula conforms to that of other didelphids is 5/4, 1/1, 4/4, 3/3. It posseses five cusps that are usually high and palatal fenestrae that are closed (Izor and Pine 1987).

Average mass: 250 g.

• Terrestrial

Black-shouldered opossum is highly arboreal and inhabits humid forests (Nowak 1991).

Terrestrial Biomes: rainforest

Black-shouldered opossums climb through trees in search of fruit in humid tropical forests and exploit nectar of flowering trees during the dry seasons. Due to their nectarivorous behaviour, they can serve as pollinators for those trees they visit. Some cranial features of Caluromysiops, such as the pronounced sagittal crest and the robust, outward bowing zygomatic arches, suggest it is adapted to biting hard substances such as nuts (Izor and Pine, 1987).

Average lifespan

Status: captivity: 7.8 years.

Reproduction in Caluromysiops is typical of the marsupials. The gestation period is short, ranging from 12-14 days. A female will often produce more young than the number of mammae available and has a tendency to lick the pouch area before birth. Little is known of the reproduction of this species. Its pattern is probably similar to that of other didelphids. In general, in this family young at birth are very small and are not as fully developed as the young of placentals. The time from birth to weaning in didelphids ranges from 110 to 125 days. (Macdonald1987).

Average number of offspring: 2.

Caluromysiops irrupta is considered the rarest of the larger didelphids, however, no special status concern has been legislated for this species (Izor and Pine 1987).

IUCN Red List of Threatened Species: least concern

Black-shouldered opossums can act as pollinators and thus aid the dispersal of seeds (Izor and Pine 1987).