MALACOSTRACA 403 



on the 4th and 5th thoracic somites, all the remaining legs subchelate, 

 and the abdomen reduced to a minute stump. 



Cyamus, the whale louse (Fig. 273 B), is a Caprella with a short, 

 wide body, adapted to its habit and habitat. 



Phronhna (Fig. 273 C), marine and pelagic, often inhabiting pelagic 

 tunicates, jellyfish, etc., is transparent and has a large head with 

 immense eyes. 



Subclass EUCARIDA 



Malacostraca with a carapace which is fused with all the thoracic 

 somites; stalked eyes; no oostegites; a short heart situated in the 

 thorax; and a large, branched "liver". 



The differences between the two orders which compose this sub- 

 class are not great. The small, prawn-like Euphausiacea are not far 

 from the lower genera of the true prawns, members of the Decapoda. 



Order EUPHAUSIACEA 



Eucarida in which the exopodite of the maxilla is small ; none of the 

 thoracic limbs are maxillipeds; there is a single series of gills, and 

 these stand upon the coxopodites of thoracic limbs; and there is no 

 statocyst. 



Fig. 282. Nyctiphanes norzoegica. Slightly magnified. From Watase. The 

 black dots indicate the phosphorescent organs. 



The Euphausiacea are marine and pelagic, and at times form an 

 important part of the food of whales. Like many pelagic animals 

 they possess (in nearly all species), phosphorescent organs, which in 

 this case are complex and situated on various parts of the body. They 

 are filter feeders. Most (perhaps not all) are hatched as Nauplii, and 

 subsequently pass through stages of the Zoaea type. 



Nyctiphanes (Fig. 282) is a British example of the group. 



