[4] All ciliates, including karyorelicteans, possess two different kinds of nucleus, which separate the functions of gene expression and sexual recombination.

In most ciliates, a macronucleus can divide during asexual reproduction to form new daughter macronuclei, through a process called amitosis.

[7] This theory has since been superseded, as molecular phylogenies have shown that the karyorelicteans are not the most "primitive" or basally-branching group of ciliates.

[8] Almost all karyorelictean species, except Loxodes, have been described from the marine interstitial habitat, where they live in the pore-water spaces between sediment grains.

[11][12][13] However, one genus, Kentrophoros, lacks an oral apparatus and feeds instead on symbiotic sulfur-oxidizing bacteria that are attached to one side of the cell.