2 U.S. NATIONAL MUSEUM BULLETIN 2 59 



Objectives 



The objective of this study is threefold: (1) to revise the systematics 

 of the subterranean amphipod genus Stygonectes based on all available 

 collections and all pertinent hterature; (2) to define, as clearly as possible, 

 the patterns of species distribution and to correlate these patterns 

 with extrinsic barriers and theoretical dispersal limits; and (3) to 

 utilize the data derived from systematics and geographic distribution 

 to construct a tenable model for explaining speciation in this genus. 



Previous to this investigation there had been no attempt to com- 

 pletely revise the taxonomy of any of the North American, fresh- 

 water ampliipod genera. The earher paper of Weckel (1907) and 

 the more recent papers of Hubricht and Macldn (1940), Shoemaker 

 (1942a), and Hubricht (1943), while all monographic in scope, did 

 not deal specifically with a given genus but covered a wide range of 

 species in a number of different genera. A more recent monograph 

 on fresh-water amphipods of this continent is that by Bousfield 

 (1958); although this paper treated comprehensively 30 species and 

 subspecies, it was geographically limited to forms known primarily 

 from glaciated North America. With the exception of short papers 

 by Greaser (1934), Mackin (1935), and Shoemaker (1938, 1942a, 

 1942b, 1945), few papers in the 20th century have dealt specifically 

 with North American, subterranean amphipods. 



JVIore than one-half of all American, fresh-water amphipod species 

 occur exclusively in subterranean waters. The taxonomy of this 

 large biota is still incompletely known, and its ecology and physiology 

 is virtually unknown. Currently, not a single Hfe history is com- 

 pletely known for an obligatory subterranean amphipod species in 

 this country. Moreover, comprehensive studies on the evolutionary 

 biology of North American, subterranean amphipods have been 

 practically nonexistent until now. 



The present study of Stygonectes is the first in a series of several 

 designed to ultimately revise, according to modern standards of 

 systematics, the six North American genera presently assigned to the 

 Crangonyx section of Gammaridae. These studies, along with ad- 

 ditional observations on several "crangonycid genera" that occiu" out- 

 side of North America, are intended to increase oiu- knowledge of the 

 systematics, zoogeography, and speciation of this group of fresh- 

 water amphipods. It is fiu-ther suggested, but perhaps a bit pre- 

 matiu-ely, that when the proposed series of revisions is completed, 

 sufficient data will be available to clearly indicate that the Crangonyx 

 section should be accorded full familial status in the suborder 

 Gammaridea. 



