 While the Malesia has much in common botanically, the portions east and west of the [[Wallace Line]] differ greatly in land animal species; Sundaland shares its fauna with mainland Asia, while the islands east of the [[Wallace line]] either lack land mammals, or are home to a land fauna derived from Australia, which includes [[marsupial]] mammals and [[ratite]] birds.The insects of New Guinea are however mainly of Asian origin.Asia also contains several important [[freshwater ecoregion]]s as well, including [[Rivers of Russia]], which flow into the Arctic, Black, and Caspian seas, Siberia's [[Lake Baikal]], the oldest and deepest lake on the planet (home to numerous endemic [[Porifera|sponge]]s, [[oligochaete]]s, and [[crustacea]]ns and the [[Baikal seal]]), [[Khanka Lake]], and Japan's [[Lake Biwa]], [[Lake Dongting]], [[Lake Tai]] and [[Lake Poyang]] in China.