The bioluminescence system of the ostracod Conchoecia pseudodiscophora, which is abundant in the Sea of Japan, has been characterized. The luminescence (lambda(max)=463 nm) is produced by a luciferin-luciferase reaction, and the luciferin has been identified as coelenterazine. Coelenterazine, coelenteramide, and coelenteramine from C. pseudodiscophora were quantified by LC-ESI-MS/MS analysis. The coelenterazine content was estimated to be approximately 230 pg per animal by using a calibration curve of synthetic coelenterazine. The reaction between homogenates of C. pseudodiscophora and synthetic coelenterazine showed luminescence activity; this suggests that a coelenterazine-type luciferase is present.