An Amphipod Crustacean. 109 



AN AMPHIPOD CRUSTACEAN 

 ( Talorchestia longicornis) . 



External Anatomy. Select a large male specimen. 

 (The males are generally larger and have antennse which 

 almost equal the body in length.) Note the laterally com- 

 pressed body and the numerous jointed appendages. Dis- 

 tinguish between the head, the thorax, and the abdomen. 



Projecting anteriorly from the head are the smaller first 

 antenna. How many joints has each? Immediately be- 

 neath the first antennae are the long second antenna. Of 

 how many joints does each consist? Compare with the 

 same organs of the female. 



Remove the head and examine from the side. Are there 

 any suture-like lines that might lead one to suppose that 

 the head is really composed of several fused segments? 

 Note the lobe-like upper lip or labnim. In what plane 

 does it move? Is there a somewhat similar organ (the 

 united first maxillipeds}, covering the mouth-parts from 

 behind? 



Remove both labrum and the fused maxillipeds. The 

 remaining mouth-parts move laterally. 



Lying immediately anterior to and under the maxillipeds 

 are the second maxilla. Each is a delicate, foliaceous, 

 bilobed organ, and bears numerous setae along its free 

 edge. 



