MALACOSTRACA 361 



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. 268. Nyctiphanes norwegica. Slightly magnified. From Watase. The 

 black dots indicate the phosphorescent organs. 



The Euphausiacea are marine and pelagic. Like many such 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. 268) is a British example of the group. 



Order DECAPODA 



Eucarida in which the exopodite (scaphognathite) of the maxilla is 

 large; three pairs of thoracic limbs are more or less modified as 

 maxillipeds, and five are "legs"; there is usually more than one 

 series of gills, of which some (podobranchiae) stand upon the coxo- 

 podites of thoracic limbs, others {arthrobranchiae) upon the joint- 

 membranes at the bases of the limbs, and others (pleurobranchiae) 



