Sea spiders of the genus Nymphon (Arthropoda: Pycnogonida) from waters around the Nansei Islands, Japan

We provide descriptions for five species in the pycnogonid genus Nymphon J.C. Fabricius, 1794 based on material from waters around the Nansei Islands, Japan. These species are: Nymphon falcatum Utinomi, 1955; Nymphon japonicum Ortmann, 1890; Nymphon nagannuense sp. nov.; Nymphon ortmanni Helfer, 1938; and Nymphon plectrum sp. nov. Examination of the paratype specimens of N. ortmanni revealed that this species has multi-pored cement glands on both the femur and first tibia, a condition not previously known. Nymphon plectrum is the 12th member of the Nymphon aequidigitatum group, for which we provide a revised key to species.