74 



ANTHOZOA 



CLASS III ANTHOZOA (ACTINOZOA) 



This Class includes the corals and sea-anemones. 

 They differ from the Hydrozoa (1) in possessing an oeso- 

 phageal tube, which is distinct from the ccelenteron, 

 though opening into it ; (2) in having the ccelenteron 

 divided up into chambers by vertical radiating partitions 

 known as mesenteries ; (3) in the reproductive elements 

 being developed in the endoderm of the mesenteries and 

 never on a medusa. 



.- 11 



Fig. 22. Semi-diagrammatic view of half a simple Coral. (Partly after 

 Bourne.) On the right side the tissues are represented as trans- 

 parent to show the arrangement of the theca and septa ; on the 

 left a mesentery is seen. 1, tentacle; 2, mouth; 3, stomodaeum ; 

 4, mesentery ; 5, mesenteric filaments, free edge of mesentery ; 

 6, ectoderm ; 7, endoderm ; 8, basal plate of skeleton ; 9, theca ; 

 10, columella ; 11, septum. 



The Anthozoa possess an apparent radial symmetry, 

 but closer examination reveals a bilateral arrangement 



