The interstitial crustacean isopods of the genus Microcharon (Microparasellidae) are relatively well-diversified and widely distributed in Morocco. A new species, M. boutini, is described. The 5-dentate mandibular pars incisiva, the elongated inner lobe of the exopodite, and the reduced armature of the first male pleopod characterize the species. M. boutini n. sp. belongs to the monophyletic messoulii group of species, the most primitive representatives of the genus. The distribution of M. boutini n. sp. covers both the northwestern part of the Jbilet and the nearest adjacent plain, as well as the High Atlas of the Marrakech piedmont. From a historical biogeographic point of view, interstitial ancestral marine populations would have been left in subterranean continental waters by the regression of the “Phosphate Sea” during the Lutetian (Eocene). The distribution of the same species both in High Atlas valleys and in the Jbilet region poses an evolutionary rate problem.

The interstitial stygobites of the genus Microcharon (Crustacea, Isopoda, Microparasellidae) are highly diversified in Morocco, especially in the High Atlas. A new species from the North Saharan platform is described. Microcharon oubrahimae n. sp. is characterized by the original morphology of the first male pleopod which exhibits a concave inner margin of the distal part and a subdistal position of the armature. From a phylogenetic point of view, M. oubrahimae does not belong to the lineage which includes the Moroccan Atlasian species. In contrast, it belongs to the eastern- Mediterranean group of species. It is related to the species of the groupM. orghidani -M. bureschi -M. phlegetonis from Romania and Bulgaria. The two-step model of colonization and evolution provides an understanding of the origin and evolutionary history of this stygobiont. M. oubrahimae derived from marine ancestors that lived in the littoral interstitial waters of the marine gulfs which covered the Errachidia-Boudnib-Erfoud basin within the pre-African trench during the Turonian or more likely Early Senonian. These marine ancestors might have settled in fresh groundwater during the regressive phases of the Turonian embayment or more likely of the brief Coniacian-Santonian gulf.