230 



Here, upon contraction of the muscles surrounding the esophagus after open- 

 ing of the cardiac sphincter, the food particles are pushed into the stomach. 

 Here the food is sorted and food particles suitable for feeding are retained for 

 some time in the anterior part of the stomach, while unsuitable particles 

 accumulate near the pyloric sphincter separating the stomach from the hind 

 gut. When the pyloric sphincter opens, the stomach contents pass into the 

 hind gut and then, after the anal sphincter opens, are egested. 



As was demonstrated by Strathmann (1971), the primary sorting may 

 occur in the oral cavity. Rejection qf food fi^om the oral cavity or esophagus, 

 or unsuitable food, is done by contracting the muscles of the esophagus and 

 oral cavity, accompanied by a change in direction of beating of the cilia of 

 the aboral band. 



Holothurian larvae can feed on microalgae of no more than 70 |a.m in 

 diameter and no more than 150 |im long. Different species of the genera 

 Phaeodactylum, Dunaliella, Amphidinium, and some others can also be food 

 objects of holothurians. The rate of filtration of algae from the water in 

 Parastichopus californicus is about 3 ml/m (Strathmann, 1971). 



Respiration, transport of metabolites, and excretion : Holothurian larvae 

 lack organs for respiration and excretion. The provisional hemal system is 

 also not formed. Transport of food substances and excretion of metabolic 

 products is effected by the fluids of the primary and secondary body cavities. 



In the early auricularia, the secondary body cavity or coelom is repre- 

 sented by the unpaired coelomic sac with the pore canal. The coelomic sac 

 soon divides into three sections; the hydrocoel and the left and right 

 somatocoels (Figure 179) (Kume and Dan, 1968). 



Figure 178: Holothuria impatiens 



(Mortensen, 1938). 

 Arrangement of ciliated bands in the 



perioral field, 

 pob — postoral band; prb — preoral band. 



Figure 179: Arrangement of coelomic sacs 



in the auricularia (Kume and Dan, 1968). 



he — hydrocoel; hp — hydropore; Is — left 



somatocoel; rs — right somatocoel. 



