The burrows of Fungiacava in the skeleton of living fungid corals are initially superficial and peripheral, later they become deep; they always open into the coelenteron. Boring is exclusively chemical, possibly by secretion of a calcium-chelating mucus by the epithelium of the pallial envelope, which surrounds the excessively delicate shell, and of the siphons. These epithelia also secrete aragonite with which all cavities in the corralum are filled and the presence of which reveals the track of the bivalve through the corallum. By the dual operation of resorption and secretion, Fungiacava always precisely fills the cavity it occupies. There is no reaction by the coral to the presence of the symbiont.