CORALS. 

 ANTHOZOA OR ACTINOZOA. 



153 



ZOANTHARIA, HEXACORALLA, e.g., 



SEA ANEMONE. 



ALCYONARIA, OCTOCORALLA, e.g. 

 DEAD MEN'S FINGERS 



Many are simple, many colonial. 



Tentacles usually simple, usually some 

 multiple of six, often dissimilar. 



Mesenteries usually some multiple of six, 

 complete and incomplete. 



Retractor muscles never as in Alcyonarla. 



Two gullet grooves or siphonoglyphes, or 



only one. 

 Dimorphism only in some Antipatharia, 



and in one Madrepore coral. 

 Calcareous skeleton if present is derived 



from the basal ectoderm. 



Types. 



Actiniaria. Sea anemones. 



Madreporaria. Reef building corals. 

 Antipatharia. Black corals. 



All colonial, except a small family includ- 

 ing Monoxcnia. and Haimea. 

 Tentacles eight, feathered, uniform. 



Mesenteries eight, complete. 



Retractor muscles always on one (ventral) 

 side of each mesentery. 



One (ventral) gullet groove or siphono- 

 glyphe, or none. 



Occasional dimorphism among members 

 of a colony. 



There are usually calcareous spicules (of 

 ectodermic origin) in the mesoglcea. 

 Examples. 



Alcyonium (Dead men's fingers), with 

 diffuse spicules of lime. 



Tubipora (Organ pipe coral), with 

 spicules fused into tubes and trans- 

 verse platforms. 



Corallium rubruin (Red coral), with an 

 axis of fused spicules. 



fszs, with an axis of alternately limy and 

 " horny " joints. 



Pennatula (Sea pen), a free phosphor- 

 escent colony, with a " horny" axis 

 possibly endodermic. 



Heliopora, blue coral. 



> S 



Z ^ A 



FIG. 48. Z, Diagrammatic section of Zoantharian ; A> of 

 Alcyonarian. (After CHUN.) 



The line 6" ^ in Z is through the siphonoglyphes (a). The 

 retractor muscles are represented by dark thickenings on the mesen- 

 teriesall on one (the ventral) side in Alcyonaria. 



Coral Making. We have already noticed that there are "corals "among 

 the Hydrozoa, viz., the Millepores. Leaving these out of account, we 

 have to recognise that both divisions of Anthozoa include many corals. 



