  In the su(2|2) spin chain motivated by the AdS/CFT correspondence, a novel
symmetry extending the superalgebra su(2|2) into u(2|2) was found. We pursue
the origin of this symmetry in the exceptional superalgebra d(2,1;epsilon),
which recovers su(2|2) when the parameter epsilon is taken to zero. Especially,
we rederive the Yangian symmetries of the AdS/CFT spin chain using the
exceptional superalgebra and find that the epsilon-correction corresponds to
the novel symmetry. Also, we reproduce the non-canonical classical r-matrix of
the AdS/CFT spin chain expressed with this symmetry from the canonical one of
the exceptional algebra.
