Deep-sea hydrothermal vent fields are among the most extreme habitats on Earth. Major research interests in these ecosystems have focused on the anomalous macrofauna, which are nourished by chemoautotrophic bacterial endosymbionts. In contrast, the meiofauna is largely overlooked in this chemosynthetic environment. The present study describes a new species, Thomontocypris shimanagai sp. nov. (Crustacea: Ostracoda), which was collected from the surface of colonies of neoverrucid barnacles and paralvinellid worms on the chimneys at the Myojin-sho submarine caldera. This is the first discovery of an ostracode from deep-sea hydrothermal vent environments in the western Pacific region. In addition to the species description, we discuss three aspects: 1) adaptation, 2) endemism, and 3) dispersal strategy of the hydrothermal vent ostracodes. Regarding these aspects, we conclude the following: 1) the new species may feed on sloughed-off tissues, mucus secretions, or fecal pellets of sessile organisms, rather than depend on chemoautotrophic bacteria as symbionts for energy; 2) as has been pointed out by other studies, Thomontocypris does not likely represent a vent-specific genus; however, this new species is considered to be endemic at the species level, as it has not been found outside of the type locality; and 3) this new species may have migrated from adjacent deep-sea chemosynthesis-based habitats, such as hydrothermal vents, with wood falls potentially having acted as stepping stones.