A molecular phylogenetic framework for the evolution of parasitic strategies in cymothoid isopods (Crustacea)

The parasitic isopods belonging to the family Cymothoidae attach under the scales, in the gills or on the tongue of their fish hosts, exhibiting distinctive life-histories and morphological modifications. According to conventional views, the three parasitic types (scale-, gill-, and mouthdwellers) correspond to three distinct lineages. In this study, we have used fragments of two mitochondrial genes (large ribosomal DNA subunit, 16S rRNA, and cytochrome oxidase I) and two species for each of the three parasitic habits to present a preliminary hypothesis on the evolutionary history of the family. Our molecular data support the monophyly of the family but suggest that – contrary to what was previously believed – the more specialized mouth- and gill-inhabiting species are not necessarily derived from scale-dwelling ones.