CHAPTER XXI 

 THE FAIRY SHRIMPS (PHYLLOPODA) 



By a. S. PEARSE 



Associate Professor of Zoology, University of Wisconsin 



Phyllopod crustaceans are among the most graceful and attrac- 

 tive of the inhabitants of fresh-water pools. A familiar example 

 is the fairy shrimp (Eubranchipus) that is a harbinger of spring 

 throughout the eastern and central United States. No phyllopods 

 are of great size, the largest usually not exceeding a couple of 

 centimeters in length, though one species of Apus reaches seven. 

 Certain genera of this group ^ of crustaceans existed in Devonian 

 times but recent species were first described by scientists early in 

 the eighteenth century, and were, with the cladoceran Daphnia, 

 made the subject of a series of remarkable memoirs by J. C. Schaffer 

 (1752-1756). Up to the present time forty-one species have been 

 described from North America and a large number from other 

 continents, for phyllopods occur in every part of the world and are 

 found from sea-level to altitudes of more than 10,000 feet. But 

 the animals that are to be discussed in this chapter are interest- 

 ing not only on account of their ancient lineage and wide distribu- 

 tion. Their primitive structure has been much studied by those 

 who sought to solve the riddle of the origin of the arthropods, and 

 their remarkable abihty to withstand striking changes in temper 

 ature and humidity, as well as the various forms that some species 

 assume under different conditions, have made them equally attrac- 

 tive to naturalists and those interested in the experimental side of 

 zoology. 



The different suborders of phyllopods present considerable 

 diversity in general shape. Such diversity is due largely to differ- 

 ences in the development of the carapace, which may form a shell- 

 fold, and these differences are curiously correlated with variations 



' Caiman rejects the suborder Phyllopoda and divides his subclass Branchiopoda 

 into four orders: Anostraca, Notostraca, Conchostraca, Cladocera. There is much in 

 fik'^ar of such a system. 



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