The present paper focuses on taxonomic and phylogenetic investigations of the family Argestidae Por, 1986. Samples, collected during the cruise DIVA 1 (M48/1) to the Angola Basin on board of RV “Meteor” (2000), contain amongst others several specimens belonging to the Mesocletodes abyssicola-group (Harpacticoida, Argestidae) which includes ten species so far. This paper deals with the description of Mesocletodes angolaensis sp. nov., M. bicornis sp. nov., M. dorsiprocessus sp. nov. and M. meteorensis sp. nov. as well as the redescription of Mesocletodes robustus Por, 1965. The four new species bear cuticular processes on the cephalothorax and/or telson, as is characteristic for the Mesocletodes abyssicola-group. These processes are supposed to be of high phylogenetic value, since they do not occur in any other taxon within the Argestidae, and are always inserted at the same position. Therefore, the Mesocletodes abyssicola-group is herein considered monophyletic.