ANTHOZOA 



145 



SUBORDER 3. MADREPORARIA.* 



The stony corals. The polyps are either solitary or colonial, and 

 secrete from the ectoderm a very hard, calcareous skeleton (Fig. 237). 

 This usually takes the form in each case of a cup into which the polyp 

 or zooid can retract itself and which consists essentially of a system of 

 radial vertical plates or septa projecting into the interior of the polyp, 

 but always covered with the three layers of the body wall and alternating, 

 in a general way, with the mesenteries (Fig. 238). The outer edges of 

 these stony septa usually join an outer wall called the theca, which is 

 the outer part of the cup in which the polyp sits. In the middle of the 

 cup is often a central column (columella). As the polyps grow, they 

 constantly build up the theca and the septa, withdrawing from the 



Fig. 237 



Fig. 237 Diagram of a coral colony (Boas). 1, extended coral polyp; 2, retracted 

 coral polyp ; 3, longitudinal section of a coral polyp ; 4, calcareous cup from which the 

 polyp has been removed ; 5, columella ; 6, septa ; 7, theca ; 8, tabulae. Fig. 238 

 Cross section of a coral, the stony skeletons being black (Boas). 1, septum ; 2, mesen- 

 tery ; 3, theca. 



deeper portions, which may become cut off by horizontal partitions 

 the tabulae. The colonies increase in size by growth and budding of 

 the polyps, producing, in this way, the coral reefs which are such an 

 important feature of tropical seas. All the reef-forming corals live in 

 shallow water, 300 feet being the maximum depth in which they are 

 found. 



The suborder contains over 1,000 species, grouped in 3 divisions. 

 Most of the species are found in tropical or subtropical waters, a few, 

 however, occurring in temperate and even in Arctic seas. 



Key to the divisions of Madreporaria: 



a v Coral porous ; septa not more than 12 1. PEEFOBATA 



a 2 Coral solid ; septa usually numerous. 



&! Septa without cross bars 2. APOROSA 



6 2 Septa with cross bars 3. FUNGACEA 



* See "The Florida Reefs," by L. F. Pourtales, Bull. Comp. Zool., Vol. 6, p. 102, 

 1880. "The Tortugas and Florida Reefs," by A. Agassiz, Mem. Am. Acad., Vol. 2, 

 1882. "The Stony Corals of the Porto Rican Waters," by T. W. Vaughan, Bull. 

 TJ. S. Fish. Com., Vol. 20, Pt. 2, p. 291, 1900, 



