  S-Heun operators on linear and $q$-linear grids are introduced. These
operators are special cases of Heun operators and are related to Sklyanin-like
algebras. The Continuous Hahn and Big $q$-Jacobi polynomials are functions on
which these S-Heun operators have natural actions. We show that the S-Heun
operators encompass both the bispectral operators and Kalnins and Miller's
structure operators. These four structure operators realize special limit cases
of the trigonometric degeneration of the original Sklyanin algebra.
Finite-dimensional representations of these algebras are obtained from a
truncation condition. The corresponding representation bases are finite
families of polynomials: the para-Krawtchouk and $q$-para-Krawtchouk ones. A
natural algebraic interpretation of these polynomials that had been missing is
thus obtained. We also recover the Heun operators attached to the corresponding
bispectral problems as quadratic combinations of the S-Heun operators
