show Abstracthide AbstractPhylogenetic linkage between host and symbionts in a multipartite symbiosis was investigated in the marine gutless annelid Olavius algarvensis. Host individuals of the dominant host mitochondrial lineages A and B, occurring in Sant' Andrea and Cavoli bays of the Island of Elba, Italy, were metagenome-sequenced. Phylogenies of host mitochondria and bacterial symbionts were re-constructed from the metagenome data.