132 



CCELENTERATA 



Fig. 219 Diagram of a longitudinal 

 section of a coral animal (Boas). 1, ten- 

 tacle ; 2, mouth ; 3, gullet; 4, mesentery ; 

 5, base of a mesentery which has been cut 

 away ; 6, septum of the calcareous skele- 

 ton covered by a fold of the foot ; 7, theca; 

 8, septum. 



CLASS 3. ANTHOZOA. (ACTINOZOA.) 



Corals, sea anemones, etc. Coe- 

 lenterates in which the polyp form 

 alone is present, no medusa gener- 

 ation appearing. The body (Fig. 

 219) is usually cylindrical in form 

 and is attached either permanently 

 or temporarily at one end, which, 

 in the sea anemones, is called the 

 foot or pedal disc. The other and 

 flattened end is the oral disc; in its 

 center is the mouth surrounded by 

 hollow tentacles, which may num- 

 ber from six to several hundred. 

 The mouth is not round, but an 

 elongated slit, at one or both ends 

 of which is a prominent, ciliated 



groove called the siphonoglyph, through which the genital products may 



reach the outside (Fig. 220). The mouth does not lead directly into the 



gastrovascular space, but into a 



tube lined with ectoderm called the 



gullet which opens into the gastro- * 



vascular cavity below. This cavity 



is divided into a number of com- 

 municating chambers by six or 



more wide longitudinal ridges called 



the mesenteries, which spring from 



the body wall and project towards 



the center of the cavity; in the 



upper portion of the body, certain 



of these mesenteries join the body 



wall with the wall of the gullet 



(Fig. 220), thus dividing this part 



of the gastrovascular space into 



small chambers which are continued 



above in the hollow tentacles, while 



in the lower portion of the gastro- 

 vascular space the edges of the mes- 

 enteries are free. 



Along the free edge of each mesentery is a convoluted thickening, the 



mesenterial filament, which is of great importance inasmuch as it contains 



2 



Fig. 220 Diagram of a cross section 

 of an anthozoan through the gullet 

 (Weysse). 1, siphonoglyph; 2, gullet; 

 3, primary mesenteries ; 4. secondary 

 mesenteries ; 5, tertiary mesenteries ; 6, 

 longitudinal muscle. 



