184 Aquatic Organisms 



The fairy shrimp, shown in the accompanying figure, 

 is one of the largest and showiest of Entomostraca. It 

 is an inch and a half long and has all of the tints of 

 the rainbow in its transparent body. It appears in 

 spring in rainwater pools and is notable for its rapid 

 growth and sudden disappearance. It runs its rapid 

 course while the pools are filled with water, and lays 

 its eggs and dies before the time of their drying up. 

 The eggs settle to the bottom and remain dormant, 

 awaiting the return of favorable season. The animal 

 swims gracefully on its back with two long rows of 

 broad, thin, fringed, undulating legs uppermost, and 

 its forked tail streaming out behind, and its rich colors 



fairly shimmering in the 

 light. 



Of very different appear- 

 ance is the related mussel- 



FIG " CM "" shrim ? (Estheria) , which has 



its body and its long series 

 of appendages inclosed in a bivalve shell. Swimming 

 through the water, it looks like a minute clam a centi- 

 meter long, traveling in some unaccountable fashion; 

 for its legs are all hidden inside, and nothing but the 

 translucent brownish shell is visible. This shell is 

 singularly clam-like in its concentric lines of growth on 

 the surface and its umbones at the top. This, in 

 America, is mainly Western and Southern in its distri- 

 bution, as is also A pus, which has a single dorsal shell 

 or carapace, widely open below and shaped like a horse- 

 shoe crab. 



These large and aberrant Branchiopods are all very 

 local in distribution and of sporadic occurrence. As 

 the seasons fluctuate, so do they. But they are so 

 unique in form and appearance that when they occur 

 they will hardly escape the notice of the careful observer 

 of water life. 



