Systematic position and phylogenetic relationships of the genera Bursaridium, Paracondylostoma, Thylakidium, Bryometopus, and Bursaria (Ciliophora : Colpodea)

The morphology and in fraciliature of Paracondylostoma cavistoma oligostria tum ssp. n. (differs from P. cavistoma cavistoma by non-overlapping morphom etric characteristics), P. setigerum chlorelligerum ssp. n. (differs from P . setigerum setigerum by having symbiotic green algae), and Bursaridium pse udobursaria were studied in live and silver-impregnated specimens. Paracond ylostoma and Bursaridium are sister groups due to a unique synapomorphy, na mely, a circumoral ciliary ribbon produced by narrowly spaced somatic kinet ids at the anterior end of the somatic kinetids. Bursaridium differs from P aracondylostoma by the euplanktonic mode of life and the paroral membrane, the middle portion of which has very loosely spaced kinetids. Based on the morphological details discovered, a Hennigian phylogeny of the genera Bursa ridium, Paracondylostoma, Thylakidium, Bryometopus, and Bursia in is propos ed. These genera are linked by four synapomorphies, namely: ( I) an apical oral opening secondarily lost in Bryometopus, which ventralized the oral ap paratus: (2) a ventral vestibular cleft occupied by the ventralized oral st ructures in Bryometopus; (3) a conspicuous adoral zone of adoral organelles ; and (4) a simple paroral membrane composed of a row of dikinetids seconda rily amplified to a conspicuous field of short, dikinetidal kineties in Bur saria, which is thus derived.