CLASS ACTINOZOA 



SEA-ANEMONES, REEF-CORALS, SEA-FANS, SEA- WHIPS, AND SEA-PENS 



THE animals of this class are divided into two subclasses, 

 based on the following anatomical differences : In the first, 

 subdivision, which includes the sea-anemones and the reef-build- 

 ing corals, the polyps have numerous simple, hollow tentacles and 

 radial partitions of the same number, both being some multiple 

 of six. The polyps of a colony are all alike, and the hard matter 

 they secrete is carbonate of lime. In the second subdivision, 

 the Alcyonaria, or halcyonoids, as they are commonly called, 

 the tentacles and radial partitions are always eight in number, 

 and the tentacles have small symmetrical appendages or branches. 

 The polyps of this group are often accompanied by small zooids 

 having no tentacles. The hard secretions are horny and elastic, 

 as in sea-fans, sea- whips, and sea-pens, or they are extremely hard, 

 as in Corallina nibrum. 



SUBCLASS ZOANTHARIA 



C" Animal-flowers") 



ORDER ACTINIAEIA 



SEA-ANEMONES 



These curious and, at times, beautiful creatures are polyps, and 

 are constructed on the radial system. They have a cylindrical body 

 with a broad base and rows of hollow tentacles around the upper 

 disk. They have a central sac, and a space between the outer and 

 inner sacs which is divided vertically by walls called mesenteries, 

 as explained on page 114. Each tentacle, however many there 



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