The irregular echinoid Clypeaster ravenelii is a conspicuous component of offshore (50-230 m depth) epibenthic communities in the northern Gulf of Mexico. Nonetheless, no information is available on its reproductive biology. Gonad condition was evaluated between November 1988 and March 1991. C. ravenelii exhibited an annual reproductive cycle with spawning in late February. Timing of gonadal production was highly consistent between years. However, the magnitude of gonadal production was much higher in 1991 than in earlier years. Annual patterns of gonadal indexes (in large part an accumulation of nutritive material) were not significantly correlated with changes in bottom sea water temperature. Annual patterns of gametogenesis and spawning were, however, highly synchronized with increasing day length during the winter. This suggests that day length may serve as an exogenous proximate cue for gametogenesis and/or spawning, at least for populations within the photic zone. Similar to most members of the genus, C. ravenelii produces copious numbers of small eggs (mean diameter =121 pm) which are slightly negatively buoyant in sea water. These characteristics are indicative of a broadcasting planktotrophic mode of reproduction. © 1993 Balaban.