MoutK 



THE PHYLA HEMICHORDATA AND ECHINODERMATA 36 J 



Anus Body cavity (coelomJ 



SKeLetal pla.fce 



Radial nerve 

 Nerue rind 



Mou-fch 



Tube f oo-fc 



Radicii canai(coeLom5) 



Proboscis 

 pore 



Collar neruZ' 



Heart 



Mouth 

 Stomochord. 



c. 



Figure 19.1. Diagrammatic representations of the Echinodermata and the Hemi- 

 chordata. A, Ventral view of a starfish (echinoderm). B, Vertical section through a starfish 

 at the position of the arrows in A. C, Lateral view of an acorn worm (hemichordate) 

 showing a few internal structures. 



Proboscis 

 pore 



Coelom, 

 Stomochord 



Pnaryroc 

 Storaa-ch 



A B 



Figure 19.2. Class Pterobranchia (genus Rhabdopleura). A, Lateral view of one 

 animal in its case (lower portion of case and stalk omitted), showing external features. B, 

 Diagrammatic section showing some of the internal organs. 



show all of the hemichordate characteristics except the gill slits, which 

 are reduced to a single pair in some species and are absent altogether 

 in others. They live mostly at considerable depths and have seldom 

 been studied alive. 



Saccog/ossus. Enteropneusts, many of which live in shallow water, 

 have been studied extensively. A familiar species is Saccoglossus kowal- 



