  We completely describe Wahlquist-Estabrook prolongation structures
(coverings) dependent on u, u_x, u_{xx}, u_{xxx} for the Krichever-Novikov
equation u_t=u_{xxx}-3u_{xx}^2/(2u_x)+p(u)/u_x+au_x in the case when the
polynomial p(u)=4u^3-g_2u-g_3 has distinct roots. We prove that there is a
universal prolongation algebra isomorphic to the direct sum of a commutative
2-dimensional algebra and a certain subalgebra of the tensor product of sl_2(C)
with the algebra of regular functions on an affine elliptic curve. This is
achieved by identifying this prolongation algebra with the one for the
anisotropic Landau-Lifshitz equation. Using these results, we find for the
Krichever-Novikov equation a new zero-curvature representation, which is
polynomial in the spectral parameter in contrast to the known elliptic ones.
