Abstract
Bivalves belonging to the families Vesicomyidae and Mytilidae, which thrive in deep-sea hydrothermal vents and cold seeps, live in symbiosis with chemoautotrophic bacteria. The present paper discusses the significance of differences in the life-styles of deep-sea bivalves and shallow-water ones, considering both those buried in the sediment and those attached to objects. The life-styles of bivalves that live buried in the sediment in shallow water are shaped by adaptations related to feeding on plankton and detritus, orientation, burrowing, and so on. Mussels living in shallow water use byssus to attach themselves to solid objects for feeding and orientation. The byssus also serves to protect them from strong wave action, preventing them from being swept off the rock surface. Deep-sea clams of the genus Calyptogena absorb hydrogen sulfide from the bottom at deep-sea hydrothermal vents and cold seeps. They do not feed on particulate matter. Deep-sea mussels of the genus Bathymodiolus attach themselves to chimneys and rocks, and to living and dead shells of the same species. Because of high hydrothermal vent activity, some of the chimneys grow 40 to 50 cm taller within a day. The surface structure of the chimneys and the temperature of their environment vary from day to day. In the case of the wave-free hydrothermal vent environment, tight attachment by byssus provides no advantage. The functional and/or ecological significance of the attachment is most likely different between shallowwater mussels and deep-sea ones.
