Nymphs of the Northeastern Nearctic species of Rhithrogena Eaton, 1885 (Ephemeroptera: Heptageniidae): Descriptions and key.

The eight northeastern Nearctic species of Rhithrogena are principally known from descriptions of male imagos. Nymphs of several species (R. amica, R. anomala, R. brunneotincta, and R. gaspeensis) remain undescribed and existing keys are incomplete or regionally restricted. The inability to accurately determine nymphs of the northeastern species of Rhithrogena has been a long-standing problem for ecologists, aquatic biomonitoring programs, efforts to monitor effects of climate on sensitive aquatic taxa, and now efforts to assess conservation needs of aquatic insect species. Nymphs of all northeastern species of Rhithrogena (except for that of R. gaspeensis, which remains unknown) are either described for the first time or redescribed in a fully comparative manner. Diagnoses for each species and a new illustrated key to late instar nymphs are presented. Two major taxonomic outcomes are: (1) clarification of the taxonomic status of R. jejuna Eaton s.s. and subsequent recognition of R. undulata (Banks) as a new subjective junior synonym of R. jejuna Eaton s.s.; and (2) recognition of a new species (R. serpenglena sp. n.) that was previously incorrectly identified as R. jejuna Eaton. Lastly, new distribution records, information on species ranges, and notes of aquatic habitats of nymphs are also presented. [ABSTRACT FROM AUTHOR]