The copulatory male of Pseudomesus brevicornis differs from the female in body form, shape of pleotelson, structure of second antenna, and in having pereiopods 5–7 with long, slender setae, modified for swimming. The immature male is similar to the female. Pseudomesus sp. recorded from 80–90 m depths off N. Greenland by Just is considered to belong to the present species. The species was found in the Norwegian Sea at depths of 1260–2105 m and in the North Polar Sea at depths of 970–1020 m. The known depth range is 80 to 2105 m. The family Pseudomesidae is discussed and it is concluded that its two genera, Pseudomesus and Micromesus, belong to Desmosomatidae and Nannoniscidae respectively, and thus the family Pseudomesidae is not considered valid.