Reproductive characteristics and strategies of reducing-system bivalves

The reproductive biology of Type 3 reducing-system bivalves (those whose pallial cavity is irrigated with water rich in reducing substances) is reviewed, with respect to size-at-maturity, sexuality, reproductive cycle, gamete size, symbiont transmission, and larval development/dispersal strategies. The pattern which emerges from the fragmentary data is that these organisms present reproductive particularities associated with their habitat, and with their degree of reliance on bacterial endosymbionts. A partial exception to this pattern is the genus Bathymodiolus, which also presents fewer trophic adaptations to the reducing environment, suggesting a bivalent adaptive strategy. A more complete understanding of the reproductive biology of Type 3 bivalves requires much more data, which may not be feasible for some aspects in the deep-sea species.