Kurma is the second incarnation of the 'Dashavatara', the ten principal avatars of Vishnu. In Hindu iconography, Kurma is depicted as a tortoise, or as a human being with a tortoise body. The number of limbs he possesses varies, as does the number of weapons he carries as a function of this. Two of his four hands carry the Shankha (conch-shell), and the Chakra (a discus), while the other two convey the Varada and abhaya mudras, gestures of charity and fearlessness respectively. On his head he wears the crown Kirita-mukuta.
Vishnu took the form of turtle to help devas and asuras ( gods and demons). They were churning ocean to create ‘amrit’ or elixir of immortality. Lord Vishnu took the form of a tortoise to act as a base to support the Mount Mandar, which was used as an axis for churning of ocean.
https://en.wikipedia.org/wiki/Kurma
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