216 



COLLEGE ZOOLOGY 



Greek mythology, but is a very successful 

 one-eyed little crustacean that lives in fresh 

 water or in the sea (Fig. 110). Cyclops 

 viridis is common in small fresh-water ponds, 

 measures from 1.5 to 5 mm. in length, and 

 is usually greenish in color. The eye is red. 

 Often on each side of the tail is a sac full 

 of eggs. Certain relatives of the cyclops live 

 in the sea; although minute in size, they are 

 often so numerous that they color the water 

 pink and furnish the principal food of certain 

 whales. Cyclops serve as the intermediate 

 host for the broad tapeworm of man and the 

 guinea worm. 



Goose barnacles (Fig. 110), so called be- 

 cause barnacle geese were once supposed to 

 have hatched from them, often attaching 

 themselves to the bottoms of ships. They are 



fringe-legged crustaceans. They were con- 

 sidered by early zoologists to be mollusks be- 

 cause they live within a calcareous shell that 

 they secrete. This barnacle possesses a long 

 stalk by which it is attached to seaweed or 

 other floating objects. It is found in both the 

 Atlantic and Pacific oceans. 



The rock barnacles, Balanus, possess a 

 thick shell but no stalk (Fig. 120). They 

 attach themselves to rocks and other sta- 

 tionary objects, to the shells in which hermit 

 crabs live, and to other animals; the body of 

 the whale often becomes intensely irritated 

 by them. When the tide goes out, they close 

 the 6 plates of their shells for protection. 

 While under water they thrust out their 

 delicate fringed legs and kick minute or- 

 ganisms into their mouths. 



Rootlike processes 

 Appendages 



Body 



-•■• Oj; 



Sacculina on crab 



Balanus (rock barnacle) 

 Figure 120. Highly magnified crustaceans. Left, rock barnacles are common marine crustaceans 

 which live permanently attached. One is shown with appendages extended and fcedmg. The 

 other is withdrawn into its shell for protection from enemies. Right, Sacculina, a curious marmc 

 crustacean, which in the adult stage is parasitic on a crab. The crab is represented by dotted 

 lines, and the parasite body from which the roots penetrate the tissues of the host by solid Imes. 



The root-headed barnacles are parasitic. 

 The best-known species, Sacculina (Fig. 

 120), attaches itself when young to a ma- 

 rine crab, between the thorax and abdomen. 



on the ventral surface. It then loses most 

 of its organs, sends rootlike processes into 

 the body of the crab, and becomes a mere 

 sac. The host's body becomes so completely 



