  The relation between Wilson and para-Racah polynomials and representations of
the degenerate rational Sklyanin algebra is established. Second order Heun
operators on quadratic grids with no diagonal terms are determined. These
special or S-Heun operators lead to the rational degeneration of the Sklyanin
algebra; they also entail the contiguity and structure operators of the Wilson
polynomials. The finite-dimensional restriction yields a representation that
acts on the para-Racah polynomials.
