In adult females of the halocyprid ostracod Conchoecia imbricata, paired saclike ovaries lie separately at the both sides of the alimentary canal in the posterior region of the trunk. The ovarian wall consists of a thin layer of the ovarian epithelium, making itself into many folds. Oogonia, very early previtellogenic oocytes, and young somatic interstitial cells are gathered in a nipple-shaped germarium in each terminal of the ovaries. In the germarium, oogonia are concentrated in the most terminal region, and very early previtellogenic oocytes are located in the remainder, arranged in order of their sizes, the larger ones nearer to the ovarian lumen. These oocytes grow and leave the germarium, not to enter the ovarian lumen, but to ride on the outer surface of the ovarian wall, sandwiched between the ovarian epithelium and its basement membrane. They grow further to mature, supported by a few tall ovarian epithelial cells and raising the basement membrane of the ovarian epithelium. The larger oocytes lie farther from the germarium on the ovarian wall. Both the basic ovarian structure and the arrangement of the early female germ cells in the germarium of C. imbricata are common to those of the podocopid ostracods, many other crustaceans, and other mandibulate arthropods, but the further growth of the oocytes on the outer surface of the ovarian wall is similar to the pattern seen in the myodocopid ostracods, the branchiurans, the pentastomids, and the chelicerate arthropods. Such an intermediate oogenetic mode in C. imbricata is unique, not only among the ostracods and other crustaceans, but also among other mandibulates and the chelicerates.