Polymorphism in gigantobacterial symbionts in the guts of surgeonfish (Acanthuridae : Teleostei)

The morphology and partial cytology of a group of bacteria-related organism s from the guts of surgeonfish are described. These gigantobacteria symbion ts are encountered in the guts of various species of this fish family throu ghout the Indo-Pacific region and the Red Sea. They have been tentatively g rouped and placed in a "family", Epulopiscidae, according to the first spec ies described, Epulopiscium fishelsoni Montgomery and Pollak, 1988. In addi tion to a morphological comparison between the various forms from different species of surgeonfish, suggestions are presented with regard to their pos sible morphological diversification during evolutionary and host-species sp ecificity.