Hyperbenthic harpacticoid samples from Japanese hydrothermal vents in the Okinawa Trough and cold seep sites in Sagami Bay were examined and resulted in the discovery of four new species belonging to three new genera of Aegisthidae (Copepoda: Harpacticoida). Females of Nudivorax todai gen. et sp. nov. possess a large area of flexible integument between the cephalosome and the first pedigerous somite which is suggestive of a gorging feeding strategy. Main diagnostic characters separating the new genus from other Aegisthidae are provided by the unusually short caudal rami, the complete lack of integumental surface lamellae, and the presence in the male of a linear array of pores along the rostral margin which appears to be sensory in function. Scabrantenna yooigen. et sp. nov. displays several similarities withAegisthus aculeatus Giesbrecht, 1891 but is highly distinctive in its male morphology which includes extremely atrophied mouthparts and a unique prehensile antenna. Jamstecia terazakiigen. et sp. nov. is only known from a single female caught in the Okinawa Trough. Jamsteciagen. nov. is most closely related to Andromastax Conroy-Dalton & Huys, 1999 but can be distinguished on the basis of the elongate antennules, the antennary morphology, the absence of lateral spinous processes on the cephalosome and swimming legs 2–4, and differences in the mandibular palp and armature of the maxilliped. Andromastax cephaloceratussp. nov. differs from the type species A. muricatus Conroy-Dalton & Huys, 1998 primarily in the presence of long spinous processes on the cephalosome and the absence of the inner seta on the female P5.