| Summary: | The super-family Eusiroidea is traditionally divided into 4 families, namely Calliopiidae, Eusiridae, Gammarellidae and Pontogeneiidae (De Broyer et al., 2007), but recent phylogenetic data suggests that the eusiroid clade forms a much broader assemblage (Englisch, 2001). Representatives are found in all oceans, inhabiting every trophic niches and a wide bathymetric range. With 216 described species in the Southern Ocean (i.e. about 24% o f its known amphipod fauna), eusiroids constitute a significant fraction of the Antarctic and sub-Antarctic biodiversity (De Broyer et al., 2007). The eusirid concept is very inadequately defined morphologically. The super-family form s a diverse assemblage of taxa o f gammaroid form , globally characterized by the loss or reduction of the accessory flagellum (Bousfield & Hendrycks 1995). The fam ily assignment of genera is often challenging, since there is no consistent set o f diagnostic characters defining most o f them. The 6 families form erly comprised in the non-validated taxon Iphimedioidea (Lowry & Myers 2000), as well as the Astyridae and Stilipedidae were recently considered as eusiroids. Moreover, previous 18S phylogenetic reconstructions revealed that the Astyridae, Iphimediidae, Epimeriidae and Pleustidae are nested w ithin the eusiroid clade (Englisch 2001). With the aim o f clarifying those major nomenclatural uncertainties and discussing the phylogenetic relationships, a deep phylogeny of the super-family Eusiroidea, including representatives o f all the aforementioned families, was reconstructed using two different gene fragm ents (28S rRNA and 1 8S rRNA). The analysis was performed at a global scale, mostly with Antarctic taxa, but also European and Arctic species. The study confirms that the Eusiroidea form s a must broader clade than claimed in classical literature. It revealed that most o f the traditionally delimited families are not m onophyletic and that a few taxa previously considered as eusiroids {Gammarellus, Cleippides) are in fact very ...
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