Systematics, Speciation, and Distribution 



of the 



Subterranean Amphipod 



Genus Stygonectes (Gammaridae) ^ 



Introduction 



Amphipod crustaceans are among the largest and least studied 

 groups of North American fresh-water invertebrates. Five famihes, 

 including Coropliiidae, Haustoriidae, HyalelHdae, Pontogeneiidae, 

 and Gammaridae, are represented in the fresh waters of North 

 America. The first four families are represented by only four genera 

 and five species; the last, however, is represented by nine genera and 

 numerous species. For further, comprehensive reviews of the 

 taxonomy and distribution of North American, fresh-water am- 

 phipods, the reader is referred to excellent treatments by Pennak 

 (1953) and Hubricht (1959). For a detailed account of the sys- 

 tematics of fresh-water amphipods of glaciated North America, the 

 thorough work of Bousfield (1958) is indispensable. 



Of the nine genera of Gammaridae with representatives in North 

 America, seven have invaded subterranean waters of which five are 

 known only from subterranean and/or interstitial habitats. Exclud- 

 ing Anisogammarus and Gammarus, which also occur in marine 

 waters, the remaining seven North American genera of Gammaridae 

 are exclusively fresh-water inhabitants and have been assigned to 

 the Crangonyx section of this family (see Schellenberg, 1936; Shoe- 

 maker, 1942a; and elsewhere in this paper). A hst of six of these 

 genera (excluding Allocrangonyx, see p. 16) and their breakdown into 

 numbers of species is given in table 1 (see p. 16). Although pre- 

 liminary studies indicate a wealth of undescribed species in the 

 Crangonyx section (especially subterranean forms), the present 

 investigation totals 29 described species in Stygonectes alone, making 

 this the largest genus of North American, fresh-water amphipods 

 known to date. 



1 A dissertation submitted in partial fulfillment of the requirements for the 

 degree of Doctor of Philosophy at the University of Kentucky. Present address 

 of the author: Department of Biology, East Tennessee State University, Johnson 

 City, Tennessee 37601. 



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