The Animal Kingdom - 643 



Fig. 32-19. Various rotifers, or "wheel animals." Despite their microscopic 

 size, these are multicellular animals with a fairly complex structure (see text). 

 (From General Zoology, by Miller and Haub. Holt, Rinehart and Winston, Inc.) 



species, originally prevalent, have since be- 

 come extinct. The Bryozoa, by forming thick 

 encrustations in shallow marine waters, co- 

 operate significantly with the corals in build- 

 ing reefs (p. 634). Petroleum geologists study- 

 ing core samples obtained from test drillings, 

 find bryozoan fossils very helpful when they 

 are searching for new deposits of oil. 



The Brachiopoda or Lamp-shell Animals. 

 Only about 200 species of these two-shelled 

 (bivalved) animals (Fig. 32-21) have survived 

 from the richly varied ancient population 



that once attached themselves to the rocky 

 bottom in shallow parts of the sea through- 

 out the world. Superficially the Brachiopoda 

 look like little oysters or other bivalved 

 mollusks. However, the valves of the brachio- 

 pods are not placed on the sides of the ani- 

 mal. Rather, there is one dorsal valve, which 

 lies above the other ventral valve. The name 

 "lamp shell" refers to the shape of the ven- 

 tral valve. This tends to resemble the ancient 

 open type of oil lamp, which once was com- 

 monly used by Greek and Roman peoples. 



