ACTINIARIA. 



189 



Section 3. Protactiniae (Protantheae). 



With 12 primary and 1 or 2 pairs of secondary mesenteries, which are dorsal 

 rather than ventral. Body-wall and oesophagus with ectodermal ganglionic 

 and muscular layers. 



Fain. Gonactinidae. Scyto2)horus R. H. ; Gonadinm Sars, with the power of 

 transverse fission ; Oractis McM. ; Protanthea Calg. 



Section 4. Edwardsiae. 



Without pedal disc, with 8 mesenteries, including two pairs of directive 

 mesenteries and 4 unpaired mesenteries (Fig. 150). All mesenteries with gonads. 

 Tentacles usually more numerous than the mesenteries. The muscular (longi- 

 tudinal) faces of the 4 unpaired mesenteries are all turned the same way. Live 

 in sand. Edwardaia Quatrefages. 



FIG. 150. Diagram of the arrangement of 

 the muscles and mesenteries of Edu'ardsia 

 (from Chun after Boveri). S, S sagittal 

 plane; a, a gonidial grooves. 



FIG. 151. Diagram of a transverse section 

 through a young Zoanthus. The section is 

 a little oblique. D dorsal, V ventral side ; 

 x gonidial groove ; c mesenteric filaments ; 

 s 1 macro-, s 2 micro-mesenteries (from 

 Perrier). 



Section 5. Zoantheae. 



With numerous mesenteries of two kinds, (a) imperfect sterile micro-mesenteries, 

 (b) larger perfect macro-mesenteries with gonads and filaments : the two kinds 

 (Fig. 151) usually placed alternately, so that each pair is composed of a larger 

 and a smaller mesentery ; two pairs of directive mesenteries, one pair consisting 

 of macro-, the other pair (dorsal) of micro-mesenteries ; one gonidial groove 

 ventral (near large directives). Usually colonial ; wall of body usually traversed 

 by ectodermal canals, and encrusted with foreign bodies which may even be 

 embedded in the wall. The longitudinal muscular faces of the mesenteries of 

 each pair are arranged as in Hexactiniae. New mesenteries are formed in the 

 inter-mesenterial space on either side of the ventral directives. The colonial 

 forms arise either from a branched stolon, or from a broad basal plate containing 

 anastomosing endodermal canals. 



Fam. Zoanthidae. Zoanthus Cuvier ; Gemmaria D. and M.; Isaurus Gray; 

 Palythoa Lamx.; Sphenopus Stenstr. , with rounded aboral end, embedded in 

 sand ; Epizoanthus Gray, often on hermit-crab gastropod shells ; Parazoanthus 

 Haddon and Shack. 



