‘ SEA ANEMONES AND CORALS 41 
form and color. They vary in size from that of a pin’s head to 
several feet across, and they live at all depths and in a great variety 
of situations. 
A coral polyp is only a sea anemone which deposits a plate of 
lime salts at the base of its barrel-like body and between the 

Fig. 16; Star-Coral Showing Living Polyps. From a Specimen in the New York Aquarium. 
radial partitions of the stomach cavity. These lime salts form 
a stony “skeleton” or substance which we commonly call “coral.” 
It is well to remember that the coral animals are not ‘“‘insects” 
but are merely sea anemones which form stony ‘ skeletons.” 
Although sea anemones and coral polyps resemble beautiful 
flowers when fully expanded, they quickly contract into a mere 
dome-shaped mass when disturbed. In this way the coral polyps 
are protected by withdrawing into their stony cup-shaped bases. 
