44 INVERTEBRATE ZOOLOGY 



CRUSTACEA 



AN ABERRANT AMPHIPOD. CAPRELLA 



This is a very common marine amphipod which is found 

 along our shores clinging to hydroid colonies and to seaweed. 

 It is an interesting form because it illustrates an extreme 

 degree of modification from the typical amphipod type; a 

 modification which is the result of its peculiar environment. 



Notice the irregular cylindrical form and the small number 

 of appendages. The apparent head is composed of seven fused 

 somites, of which five are cephalic and two are thoracic, the 

 first of these latter bearing a pair of maxillipeds, and the second 

 a pair of legs. There are thus six free thoracic segments, of 

 which the first, fourth, fifth, and sixth bear non-branchiate legs, 

 and the second and third bear gills but no legs. The abdomen 

 has lost its segmentation and its appendages and has been 

 reduced to a mere protuberance at the end of the thorax. 



Exercise l. Draw a large outline of the side view of the animal. 

 Number the segments and label the parts observed. 



Exercise 2. Construct a table of somites and appendages similar 

 to that made use of in the dissection of the crayfish or the 

 lobster. (See page 29.) 



