LAUSR

ABSTRACT Unio, a freshwater mussel genus, has a low number of species in Tunisia, among them U. durieui, which is categorised as Endangered for conservation in IUCN Red List. The purpose of the study was to investigate morphological similarity and genetic relationships between samples of the genus Unio collected from rivers of the Ichkeul watershed. The collection includes three samples of U. ravoisieri, a single sample of U. durieui and a sample morphologically distinct from the first two, which could be a new ‘species’ discovered in the sampling area. Principal components analysis, based on eight morphological traits, separated the samples into three groups according to the ‘species’ and the variant form was found morphologically closer to U. ravoisieri than U. durieui. Analysis of genetic diversity has defined an extensive allozyme monomorphism. The Nei’s standard genetic distance between U. ravoisieri and U. durieui, ranges from 0.5330 to 0.5881 and FST values vary between 0.93 and 0.98 and are highly significant. However, the genetic comparison between the variant form and U. ravoisieri samples showed no significant difference in allele and genotype frequencies, which supports the hypothesis that the new form is a phenotype of U. ravoisieri and not a separate species.