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EVOLUTION OF ANIMALS 



Part V 



It lives on muddy sea-bottoms and, climaxing its peculiarities, commonly has 

 one or more small guest clams, living in the furrows of its foot. 



The parchment worm, Chaetopterus, is six inches long (Figs. 28.13, 28.14). 

 Parchment worms secrete the tough substance of their U-shaped tubes whose 

 chimneys project above the sand at low tide. As they lie in their tubes a steady 



Fig. 28.13. Diagrams of Chaetopterus. A, animal feeding in its tube. B, dorsal 

 surface of the anterior end. 7, mouth; 2, wing-like structure from the edge of 

 which mucus is secreted; 3, mucous sac; 4, food ball, being rolled up in a ciliated 

 cup; 5, one of the main "fans" that with many smaller ones circulates the water 

 within the tube; 6, ventral suckers by which the worm holds itself to the sides of 

 the tube; 7, dorsal groove through which cilia carry the food ball toward the 

 mouth. (Courtesy, MacGinitie and MacGinitie: Natural History of Marine Ani- 

 mals. New York, McGraw-Hill Book Co., 1949.) 



Fig. 28.14. Chaetopterus glowing in the dark. (After Panceri. Courtesy, Harvey: 

 Living Light. New York, Academic Press, 1952.) 



