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 Mysis the eggs are carried in pouches under the thorax, giving 
the common name of “opossum-shrimp” to this small, transparent, 
phosphorescent crustacean. 
Mysis sternolepis. 
Genus Mysis 
M. sternolepis. About one inch in length; translu- 
cent; antennse very long; segments marked at joints 
with dark spots; the last two segments terminate in a 
stout 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 
(‘' Ten-footed "') 
The Decapoda are named from their ten walking-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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