54 LABORATORY DIRECTIONS IN 



may be cut through without opening the digestive tract. Was such a 

 cavity present in any of the preceding phyla? 



B. Economic Representatives. 



Some of the most dangerous parasites of man and other animals as 

 well as of plants are found among the Nemathelminthes. Among the 

 demonstrations are: 



5g. Ascaris, parasitic in the intestine of pigs, horses, and man. 



5h. Trichinella, which causes trichinosis in pigs, rats, and man. 



5i. Necator, the hookworm, that causes a form of anemia in human 

 beings. 



6. Phylum ECHINODERMATA (Gr. echinos = a sea-hedgehog + 

 derma = skin). 



Characteristics. 



6a. All marine. 



66. Radially symmetrical. Meaning of this expression? Verify 

 in a starfish; in a sea-urchin. (There are exceptions to radial symmetry, 

 especially in minor features.) 



6c. Parts usually arranged in fives. Verify in starfish; in sea-urchin; 

 in brittle-star. 



6dL Generally covered with spiny exo-skeleton of calcareous matter. 

 Observe in starfish; in sea-urchin; in brittle-star. Compare, however, 

 with sea-cucumber. 



6e. Possess tube-feet for locomotion. These are connected with a 

 water vascular system in the body, and operate by means of suction. 



7. Phylum ANNELIDA (Lat. annellus = a little ring.) 



A. Characteristics. 



7 a. Mode of life is terrestrial (earthworm), or aquatic (Aeolosoma, 

 fresh water; the sandworm Nereis, marine), or parasitic (some leeches). 



76. Segmented. Recall earthworm. Note also the sandworm 

 Nereis. Compare in this respect with the Platyhelminthes and 

 Nemathelminthes, which are also called " worms." 



7c. Setae. Re-examine the earthworm. How are the setae arranged? 

 Observe the sandworm, with the flattened projections at the sides of the 

 body, upon which are bunches of setae. 



B. Special Feature. 



7d. Suckers in leeches. These attach the animals to the body of the 

 host whose blood they suck. Examine any leeches available. 



8. Phylum MOLLUSC A (Lat. mollis = soft). 



Characteristics. 



8a. Body soft and unsegmented. Observe the razor-shell clam Solen, 

 Lampsilis, and Modiola, in which the shell is either open or partly removed. 



