Epulopiscium sp. type B is an uncultured Gram positive intestinal symbiont of extraordinary size (100–300 μm in length). Epulopiscium reproduces by production of internal offspring by a process related to endospore formation. Using fluorescent in situ hybridization (FISH) Hutchison et al . have followed changes in the arrangement of chromosomes. For details, see the article by Hutchison et al . on pp. 68–80 of this issue.