Investigations on the effects of the oxygen minimum zone on the distribution, abundance, and diversity of deep-sea benthic and pelagic fauna of the Gulf of California and Eastern Tropical Pacific has received attention recently. However, very little is known about the diversity of deep-sea benthic harpacticoids from this region, and only three species, Ancorabolus hendrickxi Gomez & Conroy-Dalton, 2002, Ceratonotus elongatus Gomez & Diaz, 2017 and Dendropsyllus californiensis Gomez & Diaz, 2017, have been described so far. The genus Mesocletodes Sars, 1909 is one of the most common and abundant genera of deep-sea harpacticoids. This genus has been traditionally subdivided into two species groups, the abyssicola and the inermis groups, based on the presence/absence of a dorsal cuticular process on the cephalothorax and anal somite, but some species have been reported to deviate from this scheme. As a result of their investigations, other researchers proposed the monophyly of the abyssicola group, and suggested the probable monophyly of two other species-groups. In this paper, the descriptions of three new species of the genus Mesocletodes from the deep sea of the Gulf of California are presented with some notes on their relationships with other species. Some comments on the monophyly of the genus are given.
