PELAGIC AMPHIPOD — BOWMAN AND McCAIN 



11 



When the inlets were first invaded by Cyphocaris, only those 

 individuals genetically pre-equipped to endm*e the unaccustomed 

 coastal conditions were able to siu"vive and breed successfully. As 

 the coastal popidations midtiplied in the new environment, selection 

 and adaptation proceeded until the morphologically distinct coastal 

 forms evolved. Altho immigrants continued to arrive from the 



6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 

 TOTAL LENGTH (mm) 



Figure 9. — Ratio of length of uropod 3 to that of telson plotted against body length for 

 oceanic (circles), Puget Sound (solid squares), and Revillagigedo Channel (triangles) 

 populations of Cyphocaris challengeri. 



the oceanic population, most of them could not compete successfully 

 under coastal conditions. Populations in Puget Sound and the 

 inlets of the Alexander Archipelago evolved independently and now 

 have demonstrable morphological differences. It is possible that 

 other coastal populations, now unstudied, will also show recognizable 

 differences. 



From the foregoing analysis it is clear that the northeast Pacific 

 population of Cyj^hocaris challengeri includes an oceanic form in 

 Subarctic Water and inshore forms inhabiting coastal waters of 

 western North America from Puget Sound northward. The oceanic 



