Pterygodermatites (Mesopectines) nycticebi (Mönnig, 1920) (Nematoda: Spirurida: Rictulariidae) is redescribed based on immature and mature adults collected from the stomach and small intestine at autopsy of a slow loris, Nycticebus coucang (Boddaert, 1785) (Mammalia: Primates), in a zoological garden in Japan. It is first demonstrated that male possesses a minute telamon and a left lateral pore in the preanal part of body. The cause of death of the slow loris is strongly surmised to be related to the nematode infection, which was apparently acquired under captivity in the zoological garden.