TYPES OF CCELENTERA A SEA-ANEMONE. 149 



Anthozoa or Actinozoa. 



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. 



Mesentenes usually some multiple of six, 

 complete and incomplete. 



Retractor muscles never as in Alcyonaria. 



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 in- 

 cluding Monoxenia and Haimea. 

 Tentacles eight, feathered, uniform. 



Mesenteries eight, complete. 



Retractor muscles always on one (ven- 

 tral) side of each mesentery (see 

 Fig. 66). 



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. 



Corallinm rubrutn (Red coral), with an 

 axis of fused spicules. 



/sis, 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. 



J? S 



Z A 



Fig. 66. — Z, Diagrammatic section of Zoantharian ; A, of 

 Alcyonaria n. — After Chun. 



The line S-S in Z is through the siphonoglyphes (a), the line 

 T-T passes through two interseptal spaces. The retractor 

 muscles are represented by dark thickenings on the mesen- 

 teries — all on one (the ventral) side in the Alcyonarian. The 

 line S-S in A represents the axis of symmetry. 



