Barrel Sponge

A large pink barrel sponge
(NOAA, Flower Garden Banks National Marine Sanctuary)

A barrel sponge is a great home for microbes. The sponges form symbiotic relationships with complex communities of microorganisms including archaea, bacteria and single-celled eukaryotes. The microbes carry out essential jobs that the sponge cannot do on its own, like absorbing nutrients and producing defense chemicals. In some sponges microbes can make up to 40 percent of its total weight.