OPOSSUM-SHRIMPS 257 



SUBCLASS MALACOSTRACA 



This subclass comprises highly organized Crustacea, usually of 

 considerable size, having the appendages much differentiated, the 

 thorax with eight segments, and the abdomen with seven segments, 



ORDER SCHIZOPODA 



The name, meaning " cleft-footed," applies to the appendages 

 of the thorax, which are once-branched (biramous). Gills, when 

 present, are attached to these feet, and hang freely in the water. 

 A delicate carapace covers the thorax ; the abdomen is propor- 

 tionately very large, often twice the length of the cephalothorax. 

 In Mijsis the eggs are carried in pouches under the thorax, giving 

 the common name of "opossum-shrimp" to this small, transparent, 

 phosphorescent crustacean. 



GENUS Mysis 



M. sternolepis. About one inch in length; translu- 

 cent ; antennae very long ; segments marked at joints 

 with dark spots ; the last two segments terminate in a 

 stoat spine ; telson longer than the sixth segment ; the sides are nearly 

 straight and are armed with spines ; the extremity is cleft ; eyes large 

 and prominent. Found abundantly in winter on the shores of still, 

 muddy bays and sounds, especially among eel-grass. 



ORDER DECAPODA 



C" Ten-footed ") 



The Decapoda are named from their ten walkiqg-legs. The 

 higher forms of crustaceans belong to this order. All the Decap- 

 oda have a similar anatomy, but are placed in two subdivisions 



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