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(Marmosa murina), a mammal of the family Didelphidae, order Marsupialia. The body measures approximately 13 cm in length, and the tail about 18 cm. The coloring is yellowish gray on top and lighter below. The mouse opossum has a naked, prehensile tail and lacks a brood pouch. It is distributed in South America, between the Amazon and the Orinoco rivers. It is arboreal and nocturnal and is omnivorous. The female bears as many as 15 young, which at first hang on her nipples; later the female carries them on her back. The animals feed mainly on insects and fruit.