1990 Volume 1990 Issue 160 Pages 641-662
Seven major groups of molluscan associations are recognized in the Japanese cold water molluscan faunas ranging over about 5 million years from latest Miocene to Pleistocene. Each of the groups is composed of local associations which are similar not only in species or genus composition but also in environmental preference to one another, and accordingly are in ecologically parallel relationships with one another. The distribution of the association groups was controlled primarily by water depth and grain size of bottom sediments. Each of the fossil association groups has analogous living communities comparable in their composition and habitat around Japan. Among these seven groups the Acila-Turritella Association Group is the most prevalent and is the fossil representative of the lower sublittoral community. The Delectopecten and Nuculana Association Groups are interpreted as deeper dwellers. The Anadara and Macoma-Mya Association Groups represent shallow marine environments, comparable with sandy and muddy upper sublittoral faunas, respectively. Occurrence of the Thyasira Association Group may be related to a reducing environment. The Chlamys Association Group occupied coarsegrained sand bottoms of the lower sublittoral or upper bathyal zone.