302 Animal Biology 



or arms not sharply marked off from the central disk. The internal visceral 

 organs extend into the arms. There is a distinct ambulacral groove on the ven- 

 tral side of the arms. There is a true coelom (body cavity). The body is some- 

 what flattened. The anus and madreporite plate (entrance of water vascular 

 system) are located on the dorsal, upper aboral side. 

 Example: Starfish (Figs. 104 to 107 and 328). 



MADREPORITE 



STONE CANAL 



RING CANAL 



TIEDEMANN'S BODIES 

 LATERAL CANALS 



Fig, 106. — Water-vascular system of starfish somewhat diagrammatic. The 

 madreporite is a porous plate on the upper surface of the starfish, between the 

 bivium rays, through which the water enters. The ring canal is also known 

 as the circular or circumoral canal. There are nine Ticdemann's bodies (the 

 tenth is replaced by the stone canal), which produce the amoebocytes found in 

 the fluid within the water-vascular system. The lateral canals are also known as 

 connecting canals. (From Parker and Clarke: An Introduction to Animal Biol- 

 ogy, The C. V. Mosby Co.) 



OSSICLE 



BODY WALL 



AMBULACRAL RIDGE 



" OSSICLE 



RADIAL CANAL 



LATERAL CANAL 



COELOM- 

 AMBULACRALGROOVE 



ADAMBULACRAL OSSICLE 



PAPILLA 



DERMAL BRANCHIA 



PYLORIC CAECA 



PEDICELLARIA 



AMPULLA 

 RADIAL NERVE 

 GONAD 



PERITONEUM 



TUBE FOOT 



AMBULACRAL 

 SPINE 



Fig. 107. — Cross section of a starfish arm or ray, somewhat diagrammatic. (From 

 Parker and Clarke: Introduction to Animal Biology, The C. V. Mosby Co.) 



