64 



COELENTERATA 



sume." The gastrovascular cavity is divided by thin double mesen- 

 teries into six radial chambers. Other shorter mesenteries, not at- 

 tached to the digestive tube, incompletely divide the cavities still 

 further. Near the base of the coelenteric chamber (gastrovascular 

 cavity) there are two types of mesenterial filaments. The first are 

 secretory in function, while the second, the acontia^ are provided with 

 gland cells and nematocysts. The acontia may be shot out through 

 the body wall of an irritated anemone until the mass of white threads 

 conceals the bottom of an aquarium jar. Italians eat certain sea 

 anemones, terming them " ogliole." 



Fig. 27, Corals. (Courtesy of American Museum of Natural History.) 



Corals. — The coral polyps resemble the sea anemones in their 

 internal structure, having an esophageal tube, mesenteries, and 

 internal gonads. Unlike the anemones, they form colonies^ and have 

 leathery, calcareous, stony, or horny skeletons of ectodermal origin. 

 In the red coral, originally separate spicules become embedded 

 in a cement-like deposit of calcium carbonate, forming a hard 

 branched rod which serves as an axis for the colony. Members of a 

 coral colony are connected, each individual securing its own food. 



