SECTION I 

 INTRODUCTION 



It is obvious from the number of species represented in this key that 

 very little is known about North American freshwater polychaetes. The 

 number of freshwater species in the world is quite small when compared 

 with the vast number of marine species. There are several marine forms 

 which have penetrated brackish and fresh water but remain unable to breed 

 there while others have adapted sufficiently to remain for their entire 

 life span. Of the some 60 polychaete families, only seven have been re- 

 ported as having freshwater representatives. These are the Nereidae, 

 Nephthyidae, Lumbrineridae, Spionidae, Capitellidae, Ampharetidae, Sabel- 

 lidae and Serpulidae (Wesenberg-Lund, 1958) , The largest number of fresh- 

 water species are of the families Nereidae and Sabellidae, the others hav- 

 ing fewer than five representatives. All freshwater representatives are 

 from well established marine families and have not required the establish- 

 ment of any taxon higher than genus. The Nereidae, with the largest number 

 of freshwater species, are known for their ability to withstand extreme 

 salinity changes and have been widely used as experimental animals in 

 salinity tolerance work. This paper is not concerned with those worms re- 

 ported to withstand fresh water in the laboratory, but only with those 

 actually collected from fresh water. Some of the species included in this 

 paper are strictly freshwater forms while others are euryhaline. 



Of the known freshwater species, the majority are from South America and 

 Asia with only a small proportion having been collected in North America. 

 There have been several papers dealing with freshwater polychaete species 

 and comprehensive surveys were made by Wesenberg-Lund (1958), Southern 

 (1921) and Stammer (1932) . It is very probable that there are many more 

 species present and that our lack or knowledge is due to their small size 

 and to the scarcity of collections made with polychaetes in mind as well 

 as the scarcity of specialists willing to work with them. Eight species, 

 representing six genera are included in this paper. Several species are 

 in monotypic genera but the majority are in typical marine genera. The 

 species list in this paper includes three families: Nereidae with six 

 species; Sabellidae with one species; Serpulidae with one species. 



