310 



COLLEGE ZOOLOGY 



The water-vascular system consists of a 

 madreporite, a stone canal, a ring canal, and 

 5 radial canals which extend meridionally, 

 connecting with the tube feet (Fig. 195). 

 Transverse canals leading to the tube feet 

 and ampullae are given off by the radial 

 canals. Respiration takes place in most 

 echinoids through 10 branched pouches 

 situated on the area surrounding the mouth. 

 Echinocardium is a heart-shaped urchin, 

 and Echinarachnius resembles a silver dollar. 

 Sea urchins are variously colored; they may 

 be white, purple, green, yellowish green, 

 gray, black, etc. Some species possess very 

 long poisonous spines, such as Diadema of 

 Florida and the West Indies. 



Sea cucumbers 



The sea cucumber differs from other 

 echinoderms in that it has an elongated 

 body, and lies on its side. One type of sea 

 cucumber (Fig. 190) sometimes used for 

 study is Cucumaria frondosa. This species 

 is abundant on the coast of Maine. Sea 

 cucumbers live sluggishly on the sea bottom 

 or burrow in the surface mud or sand with 

 only the ends exposed. Instead of a test or 

 skeleton of spine-bearing plates, Cucumaria 

 has a muscular body wall containing very 

 small calcareous plates. The digestive tract 

 (Fig. 196) consists of a mouth, a short 

 esophagus, a small muscular stomach, and a 



Radiat canal 



longitudinal muscle' 



Madreporife 

 Esophagus 

 Genital duct 

 Stomach 

 Gonad 



Tentacles 

 Mouth 



Retractor muscle 

 Ring canal 

 Polion vesicle 



Longitudinal muscle 

 ■Ampullae 



Figure 1%. Sea cucumber, Cucumaria, showing the tube feet and internal structure. 



