Taxonomy and seasonal diversity of Nile molluscs are important to understand the ecological impact of these animals on sustainability of River Nile ecosystem dynamics. The present work aims to explore and evaluate the taxonomy and diversity of four benthic molluscan species; two gastropods and two bivalves, in three of Egyptian irrigated Nile channels (Rayahs). The specimens were collected seasonally during the period from spring 2014 to winter 2015.Taxonomy of specimens were studied from the views of morphology and 18S rRNA gene analysis. The Gastropod species-1 and-2 had 5-6 light or dark brown whorls, but the last whorl of Gastropod sp.-2 was larger than that in Gastropod sp.-1. The phylogenetic analyses of 18S rRNA gene showed that both of Gastropod species formed monophyletic cluster, which had paraphyletic lineage with species Viviparus georgianus, implicating two new species under the genus Viviparus. The shell of the Bivalve sp.-1was ovoid with light greenish brownish or yellowish color, while the Bivalve sp.-2 had light brown to grayish elongated shell. Both of Bivalve spp.-1and-2 showed 18S rRNA gene sequence identity; averages of 89% and 92%, respectively, with Lampsilis cardium suggesting new genera within the family Unionidae. Gastropod sp.-1 showed highest abundance, during winter in El-Rayah El-Tawfiky, while the lowest was recorded during spring in El-Rayah El-Behery. Gastropod sp.-2 was abundant during summer in El-Rayah El-Behery. The seasonal distribution of the two studied bivalves declared the highest abundance in both of El-Rayah El-Behery and El-Rayah El-Tawfiky during winter, while declined during spring in all Rayahs.

Macrobenthic invertebrate communities serve as markers of anthropogenic stress in freshwater ecosystems. In this study, 17 sampling sites were selected from two Nile river subbranches (El-Rayah El-Behery and El-Rayah El-Nassery) and subjected to different anthropogenic influences to explore the ecological environment and characteristics of macrobenthos communities. Macrobenthos were studied using taxonomic diversity and biological trait analysis to investigate how human activity and variation in water quality affect their structure and function. A total of 37 taxa represented by 43,389 individuals were recognized. The communities are composed chiefly of Oligochaeta and aquatic insects. Multivariate statistical analyses found that the most influential environmental variables in the structural and functional community were sodium, dissolved oxygen, silicate, pH, calcium, and cadmium. At high levels of pollution, notably sewage and industrial pollution in the northern part of El-Rayah El-Behery, characteristics such as larger body size, detritus feeders, burrowers, and high tolerance to pollution predominated, whereas at low levels of pollution, features such as small body sizes, scraper and predator feeders, intolerant and fairly tolerant of pollution, and climber and swimmer mobility are predominant. The results confirm our prediction that the distribution of macroinvertebrate traits varies spatially in response to environmental changes. The diversity-based method distinguished impacted sewage and industrial sites from thermal effluent sites, while the trait-based approach illustrated an apparent variance between the ecological status of contaminated regions. Therefore, the biological features should be employed in addition to structural aspects for assessing the biodiversity of macroinvertebrate communities under environmental stressors.