196 ANIMALS WITH JOINTED LEGS— THE ARTHROPODS 



game and food fish. In size and general body shape they resemble 

 fleas (insects), but their body structure is entirely different. 



Cyclops was a huge giant with a single eye in the center of his fore- 

 head according to Greek mythology, but according to a zoology text- 

 book the cyclops is just another small crustacean about the size of the 

 water flea. It certainly does not resemble the mythical Cyclops in size, 

 but it does have a single eye in the center of the head region. 



The pill bug, or sow bug, is another crustacean. It differs from the 

 others studied in that it spends its life on the land. Like all crustaceans, 

 however, it breathes by gills, but is able to exist on the land by coming 

 out only when the air is very moist, which is usually at night. During 

 the day it gets under rocks, logs, or similar structures where the humidity 

 is high and the air cool. Its name is derived from the habit of rolling 

 into a tight little ball when disturbed which makes it appear somewhat 

 like a little pill. Sometimes pill bugs are quite destructive to garden 

 plants and poison must be put out to kill them. 



Classification and Derivation of Words 



Phylum Arthropoda (Gr. arthron, joint; pons, foot; refers to the jointed 

 condition of the appendages). 

 Class Crustacea (L. criista, crust-like covering; refers to the crust-like 

 exoskeleton). 

 Genus Cambarus (Gr. kammaros, crayfish). 



Other examples: lobsters, crabs, shrimp, barnacles, water fleas, Cy- 

 clops, and pill bugs. 



REVIEW QUESTIONS 



1. List the points that indicate that the arthropods are a very successful group 

 of animals. 



2. Give the characteristics of the Arthropoda. 



3. What are the advantages and disadvantages of the endoskeleton as compared 

 to the exoskeleton? 



4. What is a biramous type of appendage? Name the parts of a typical 

 biramous appendage. 



5. What is the meaning of the terms homologous and analogous? 



6. Describe the entire digestive process in the crayfish. 



7. Compare the open with the closed type of circulatory system. 



8. Can you think of a good reason why the flexor muscle of the crayfish is 

 so much larger than the extensor muscle? 



9. Explain how the sense organ of equilibrium functions in the crayfish. 



10. Compare the function of the swimmerets in the male and female crayfish. 



11. How do the fairy shrimp pass through the dry summer months? 



12. What is the economic importance of barnacles ? 



13. The pill bug lives on land yet it uses gills for respiration. Explain. 



