Nutritional symbiotic associations between marine invertebrates
and intracellular sulfur-oxidizing bacteria have been
characterized for over 2 decades (15, 18). Chemoautotrophic
symbiosis was first described in invertebrates living at the hydrothermal
vents but is now known to occur in invertebrates
from more accessible habitats, such as shallow-water sediments
(4, 43). Since their discovery, only one chemosymbiotic animal,
the shallow water lucinid Codakia orbicularis (20, 22), has been
successfully reared to the juvenile stage without symbionts.
This species belongs to the Lucinidae, one of five bivalve families
known to have a symbiotic relationship with intracellular
chemoautotrophic bacteria (reviewed in references 18 and 44).