THE CLASSIFICATION OF CRUSTACEA 53 



Gammarus pulex, sometimes called the ** Fresh-water 

 Shrimp," which is found everywhere in streams 

 and ditches. Several closely allied species, such as 

 G. locusta (Fig. 21), are found in the sea. The body 

 is flattened from side to side, and the abdomen is 

 generally bent upon itself. There is no carapace, 



vm 



Fig. 21 — An Amphipod {Gaynmarus locusta). Enlarged. (From 

 Lankester's "Treatise on Zoology," after Sars.) 



a', Antennule ; a", antenna ; ace, accessory (inner) flagellum of anten- 

 nule ; br, gill plate ; ex, coxal plate (the expanded first segment 

 of the leg) ; gn, the two pairs of gnathopods (prehensile legs) ; 

 pip'", abdominal appendage of third pair ; prp', prp", first and 

 second peraeopods, or walking-legs ; t, telson ; tir, uropod ; II, 

 VIII, second and eighth thoracic somites; i, 6, first and sixth 

 abdominal somites 



but, as in the Isopods, the first thoracic somite is 

 fused with the head. The eyes are sessile on the 

 sides of the head. The antennules have a small 

 inner branch, and the antennae have no exopodites. 



