ABSTRACT: Bythograea laubieri, B. vrijenhoeki and alvinellid polychaetes dominate the vent fauna of the Pacific-Antarctic Ridge. We studied gonadal development in females of both crabs. They have ovary microstructures characteristic of brachyuran decapods. The ovaries are paired organs overlying the hepatopancreas beneath the carapace. Oogonia proliferate from the germinal epithelium and develop into previtellogenic oocytes that grow to 60 μm before undergoing vitellogenesis. The observed maximum sizes of mature oocytes were 209 μm in B. laubieri and 138 μm in B. vrijenhoeki. No ovigerous females were found in the samples, which agrees with the segregation behaviour of ovigerous females away from the direct influence of the active chimney in some related species. In contrast to other species of bythograeid crabs, the oocyte size-frequency data suggest that B. laubieri and B. vrijenhoeki lack synchrony in reproduction of the population as a whole. Synchrony and seasonality in reproduction of B. thermydron have been linked to the formation of phytoplankton blooms in surface waters. We suggest that the biogeography of bythograeid crabs is determined by contrasting oceanographic regimes that influence the reproductive patterns observed in different species.