V*^iA 



m:-- 







s 



"v,^ 



y^y 



c-^l*^ 



The Cassiopeia at the left is swimming, and the one at the right is lying on its back in feeding 

 position, with the branching many-mouthed lobes gathering food particles. ( Lerner Marine 

 Laboratory, Bimini. Fritz Goro: Life Magazine) 



of the polyp is not conical, as in many hydrozoan 

 polyps, but is expanded into a flat disk that has an 

 oval or slitlike mouth at the center and bears one or 

 more circlets of hollow tentacles. The external cover- 

 ing layer turns in at the mouth to form a tube, the 

 gullet, which hangs into the digestive cavity. The gul- 

 let is lined with beating flagella and usually has one 

 or two flagellated grooves that direct currents of wa- 

 ter to the inside. Unlike the simple cavity of hydro- 

 zoans, that of anthozoans is divided by membranous 

 partitions, all or some of which extend from the body 

 wall to the hanging gullet. 



The class Anthozoa is divided into two groups: 

 the alcyonarians or octocorallians, in which all the 

 parts are based on a plan of eight; and the zoanthar- 

 ians or hexacorallians, in which the body is based on 

 a plan of six, or of a multiple of six, or on some 



other number, but not on a plan of eight simple re- 

 peated parts. 



THE ALCYONARIANS 



(Subclass A Icyonaria) 



Alcyonarians are all colonial growths, often color- 

 ful and luminescent, and they are especially conspic- 

 uous in warm seas. At a distance they show great va- 

 riety of shape, most of them arising from the bottom 

 as fleshy lobes or as slender branched feathers or 

 fans. Except for the gorgonians, they are mostly 

 rather insensitive to light, and they respond to touch 

 only locally, though in a few forms the stimulus 

 spreads for some distance over the colony. Those 

 that are not permanently attached, like the sea pens, 

 are the most responsive. Some that pay no heed to 

 probing fingers will react to chemical or electrical 



98] 



