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The ecology and life history traits of Boreomysis oparva, a recently described benthopelagic mysid,were examined from the seamount Volcano 7 which penetrates into the oxygen minimum zone. In the near-bottom waters, B. oparva was very abundant at the lower summit in the oxygen minimum zone (<0.2 ml O2 l-1). It decreased in abundance with increasing depth and increasing oxygen at the flank and was absent from the base of Volcano 7. Length distribution of free-living stages was continuous, from 4 to 26 mm, and similar at the lower summit and flank. This and the presence of larvae of all stages suggest continuous rather than seasonal reproduction. Reproductive females with developing larvae were more abundant at the lower summit than the flank. This new oxygen minimum zone mysid has relationships of egg volume and clutch size to female body length similar to other meso- and bathypelagic mysids.