MARINE GAMMARIDEAN AMPHIPODA 31 



Interfamilial Gammaridean Relationships 



Through reeapitulation of the general evolutionary trends within 

 the Gammaridea, one may estimate the pattern of evolution and rela- 

 tive positions of the several families (graph 1). Formulation of this 

 pattern was assisted by organizing data on 3-dimensional stick charts 

 containing plots of characters representing grades of structure, and 

 simple character alternatives; on wheels and triangles so as to demon- 

 strate presence or absence of characters in small familial groups; 

 by determining the fewest logical increments of change necessary to 

 transform one family into another. The final pattern was influenced 

 strongly by ampliative inference in using our knowledge of the ex- 

 treme members of a family plus the implication that some changes 

 require more genetic input than others even though genetic "revolu- 

 tions" may occur repeatedly in certain groups and that certain gross 

 characters are very stable. 



Only position and change from one condition to another could be 

 incorporated in graph 1 ; thus each family appears falsely to have equal 

 importance to all others. Estimates of distance might be incorporated 

 as a measure of genetic input; generic and specific diversity of the 

 famUial centers could be shown by reducing the graph to an areal 

 projection reflecting the harmony of certain grades of structure (at 

 least in widespread families tested by a wide range of environmental 

 selection) and the low level of diversity in famflial "experiments." 

 The pattern has been organized to fit the space although distance from 

 Gammaridae implies specialization or advancement. At best, the 

 pattern is a straw man. 



Graph 1 has been partitioned into more than a dozen blocks of one 

 or more families (or genera). Some of those blocks, like the Colo- 

 mastigidae or Lysianassidae, have uncertain relationships to other 

 Gammaridea. Solid arrows represent estimates of strong and direct 

 relationships; arrows commencing between two families or at long 

 distances from family groups imply relationship only to ancestral 

 pools having grades of structure similar to existing families. Dotted 

 lines imply weak or distant relationships; wavy lines denote families 

 placed close to Gammaridae because of precedential pathways 

 established in adjacent examples. Symbols on the chart are reminders 

 of certain characteristic structures and are cumulative between 

 arrows unless marked otherwise. 



The Gammaridae form the base stock and eight other families are 

 enclosed within the block denoting gammarid-like structure, two 

 families, the Phoxocephalidae and Haustoriidae, being so close to 

 Gammaridae as not to warrant extra space on the diagram. They 

 have extreme f ossorial adaptations , found rudimentarily in several 

 Gammaridae. 



