Tortoise is 1 of the 9 treasures of Kuvera.
Black Tortoise North, Winter, Black, Water
The tortoise, as in China represents the microcosmic or lower hemisphere of the zodiac. The toad-serpent forms the upper macrocosmic half. http://members.aol.com/maatmythology/part10.htm
Among Yoruba signifies craftiness.
China: Gui Xian Kwei http://infomotions.com/etexts/gutenberg/dirs/1/5/5/1/15516/15516.htm