142 COLLEGE ZOOLOGY 



ectoderm cells. Examples: Astrangia (Fig. 86), Oculina (Fig. 

 90), and Madrepora. 



Most of the stony corals belong to this order. Astrangia 

 has already been described (p. 137, Fig. 86). Oculina (Fig. 90) 

 and Madrepora are branching corals. Meandrina (Fig. 91) is 

 a more compact " brain " coral. Many of the coral polyps are 

 tinted with pink, lilac, yellow, green, violet, red, etc., and give 

 the coral reefs the wonderful color effects for which they are 

 famous. 



Order 4. Zoanthidea. — Zoantharia usually colonial; only 

 one siphonoglyphe ; mesenteries differ from those of Actiniaria ; 

 no skeleton, but often incrusted by sand. 



Certain Zoanthidea are the black corals of the Mediterranean ; 

 others live symbiotically with hermit crabs or sponges. 



Order 5. Antipathidea. — Colonial Zoantharia with a horny, 

 usually branching axial skeleton, but no calcareous spicules. 



The corals belonging to this order are found in all the large 

 seas, usually at a depth of from fifty to five hundred fathoms. 



Order 6. Cerianthidea. — Solitary Zoantharia without 

 a skeleton ; one siphonoglyphe ; no bands of retractor muscles on 

 mesenteries. Example : Cerianthus. 



This order contains a single genus, Cerianthus. One species 

 C. americanus, occurs on the eastern coast of North America: 

 other species occur in widely separated localities. 



5. COZLENTERATES IN GENERAL 



Definition. — Phylum Ccelenterata. — Polyps, Jelly- 

 fishes, Corals. — Diploblastic, radially symmetrical animals, 

 with four or six antimeres; a single gastro vascular cavity; no 

 anus; body -wall contains peculiar structures known as nemato- 

 cysts or stinging cells. 



Morphology. — The foregoing account has shown that ccelen- 

 terates all possess a body-wall composed of two layers of cells, 

 an outer ectoderm and an inner entoderm. They are therefore 

 diploblastic, although many Anthozoa have a fairly well de- 



