The ciliates form a symbiosis with sulfur-oxidizing chemosynthetic bacteria of the species "Candidatus Thiobios zoothamnicoli", which live on the surface of the colonies and give them their unusual white color.

[3] Like in other ciliates, a contractile vacuole maintains osmotic balance for the cell, and allows it to survive the salt concentrations in both marine and brackish water.

Most ciliates live as single-celled organisms in aquatic environments, and the single cell carries out all functions of life, such as nutrition, metabolism, and reproduction.

For example, plant material like the torn-off leaves of Posidonia oceanica in seagrass meadows of the Mediterranean accumulate in depressions of rocky ledges and decompose.

Because there is little water current under mangrove roots and at seagrass deposits under rock ledges, these decomposition hot-spots are extremely poor in oxygen and rich in sulfide.

The Zoothamnium colonies do not settle directly over the decomposing material, but nearby e.g. on overhanging rocks, leaves of seagrass or seaweed, or mangrove roots.

[3] The symbiotic benefits provided by the colonies of Z. niveum for its attached ectosymbiotic bacteria Candidatus Thiobios zoothamnicoli (a member of the Gammaproteobacteria[4]), which are vertically transmitted to its host,[8] are its active alternation between oxygen-rich and sulfide-rich conditions.

This alternation can occur through the regular contraction and extension of the colonies and through the water currents set up by the beating of the cilia in the region of the oral opening of the ciliates.

[9] The rapid contraction and slow re-extension of the colonies causes a flow of both sulfide-rich water for the feeding of the bacteria and normal oxygenated seawater for the respiration of Z. niveum.