Small metazoan-microbial reefs, massive, barrel- to lens-shaped bioherms a few meters high and 2–5 meters across. in situ biotic builders are microbialites (mainly thrombolites) and lithistid, calathid, and pulchrilaminid sponges; many are dominated by thrombolites, some are dominated by Calathium, and a few are dominated by lithistid sponges.