ABSTRACT

This chapter shows that the microbial symbionts have been shown to have a free-living stage and provides examples of mutualistic interactions with multicellular animals that illustrate their importance in marine ecology. It explains about symbioses of marine invertebrates through the application of modern techniques, the interactions show many parallels with the interactions between pathogenic bacteria and their hosts. Thyasirid clams oxygenate marine sediments with help from magnetotactic, thiotrophic symbionts. Sponges are the oldest group of multicellular animals, comprising more than 8000 species in a wide variety of tropical, temperate, and cold-water marine habitats, with a smaller number of freshwater examples. The discovery of chemosynthetic symbionts in animals from hydrothermal vents was quickly followed by their detection in methane cold seeps. Crustaceans have also been shown to host chemosynthetic episymbionts. In addition to the gammaproteobacterial chemosynthetic endosymbionts, Bathymodiolus spp. have been shown to harbor bacteria belonging to the Epsilonbactereota phylum.