304 CLIMAX OF THE ANIMAL KINGDOM— PHYLUM CHORDATA 



detail in a general course in zoology, but they are listed here in order 

 that our survey of the animal kingdom will be complete. 



Subphylum 1. Hemichordata. A typical representative of this 

 group is the acorn worm, Balanoglossus. This is a primitive, worm-like, 



Photo by Winchester 



Fig. 21.4. A sea squirt, tunicate. This primitive chordate is little more than a bag 

 with siphons for sucking in and squirting out the water in which it lives. However, its 



larva has typical chordate characteristics. 



burrowing animal. At the anterior end of the body there is an egg-shaped 

 proboscis which fits into a collar which is immediately posterior. This 

 gives the anterior end of the body an appearance somewhat like an acorn 



