Marine sponges often form symbiotic relationships with bacteria that fulfil a specific need within the sponge holobiont, and these symbionts are often conserved within a narrow range of related taxa. To date, there exist only three known bacterial taxa ( Entoporibacteria , SAUL , and Tethybacterales ) that are globally distributed and found in a broad range of sponge hosts, and little is known about the latter two.