| The upper part of the polyp secretes an exoskeleton of
calcium carbonate, the "polypierite" (Figure 5). The lower part
of the polypierite has a calcareous blade, the basal layer, from which the
theca rises vertically. These two elements delimit a cavity, the lumen,
divided by calcareous divisions, the septa, which are prolonged along the
sides to exterior of the theca. The axial part of the polyp has a vertical
skeletal structure, the columel. The upper part of the polypierite, delimited
by the theca, is called a calice. The lumen is also divided transversally
by calcareous plates which form the endotheca. In colonial polyps, the thecae
are joined by the cœnosteum or exotheca, synthetised by the cœnosarc. |
