Note
We report here the in vitro rearing of embryos of the deep-sea echinoid Echinus affinus col1ected from 2,000 m in the NE Atlantic Ocean. Embryos developed more rapidly at the pressure equivalent of 2,000 m than the pressure equivalentof 1,000 m, which is near the upper limit of the bathymetric range of this species, At atmospheric pressure and at the pressure equivalent of 500 m fertilization membranes formed and nuclei cleaved' but cytoplasmic division was inhibited. These findings suggest that embryonic pressure requirements could set the upper bathymetric limits of some deepsea species.