 The septa, palliform lobes and costae can often be seen through the coenosarc, the layer of living tissue that covers the coenosteum, the part of the skeleton between the corallites.In colonial species, when the corallites each have a surrounding wall, the colony is said to be "plocoid".When the walls are tall and tubular, the colony is "phaceloid", and when several polyps share a common wall, the colony is "cerioid".