Trachelocercidae is the largest family within the Karyorelictea with about 70 nominal species so far described.
Description
Trachelocercids usually have an elongated body, which may be divided into head, neck, trunk and tail regions, an apical oral cavity, and most have several macronuclei and micronuclei arranged in nuclear groups
12Ma, Mingzhen; Xu, Yuan; Yan, Ying; Li, Yuqing; Warren, Alan; Song, Weibo (2021). "Taxonomy and molecular phylogeny of four karyorelictid species belonging to the genera Apotrachelocerca and Tracheloraphis (Protozoa: Ciliophora), with descriptions of two new species". Zoological Journal of the Linnean Society. 192 (3): 690–709. doi:10.1093/zoolinnean/zlaa109.
↑Foissner, W.; Al-Rasheid, K. A. S. (1999). "Updating the trachelocercids (Ciliophora, Karyorelictea). VI. A detailed description of Sultanophrys arabica nov. gen., nov. spec. (Sultanophryideae nov. fam.)". European Journal of Protistology. 35 (2): 146–160. doi:10.1016/S0932-4739(99)80032-7.