Each stoma of a leaf is bordered by a pair of cells that open and close the pore. What are those cells called?

Explanation

The pore itself is only a gap; it is the pair of cells on either side of it that change shape to widen it or close it again. The cells named after the surface layer make up the rest of that layer and do no such thing, and the sugar-making layers lie deeper inside the leaf where there are no pores.