Coenenchyme

Coenenchyme is the common tissue that surrounds and links the polyps in . It consists of mesoglea penetrated by tubes (solenia) and canals of the gastrodermis and contains sclerites, microscopic mineralised spicules of silica or of calcium carbonate. The stiff projecting portion of coenenchyme that surrounds each polyp is usually reinforced by modified sclerites and is called the calyx, a term borrowed from botany. "Coenosarc" is an alternative name.

...
Wikipedia