Ecological and Taxonomical Characterizations of some Molluscan species in Irrigated Nile Channels, (Rayahs), Egypt

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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 Gastropodsp.-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 Bivalvesp.-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.

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