Abstract
Retortamonadida (retortamonads) is a group of bacterivorous metamonads belonging to Fornicata, currently represented by the single family Retortamonadidae, with two genera, Retortamonas and Chilomastix, and about 60 species. They are adapted to low-oxygen environments and live predominantly as endocommensals in intestines of animal hosts, including humans.
Two species were reported to be potential pathogens causing diarrhea in humans (C. mesnili) or unadapted avian hosts (C. gallinarum). One species (C. cuspidata) is free-living in hypoxic water sediments.
Retortamonads are typical excavates with a single karyomastigont possessing four basal bodies and two or four flagella. One flagellum is recurrent, has two or three lateral vanes, and is associated with a ventral feeding groove.
Double-membrane-bounded organelles without cristae, assumed to be mitochondrial derivatives, were found in Chilomastix. Retortamonads reproduce by binary division and produce a resistant cyst stage.
The cysts of endobiotic species are discharged with feces and serve to spread the infection. Recent phylogenetic analysis and ultrastructural observations indicate that Retortamonas species from insects are close relatives of Chilomastix, while species from vertebrates appear to be relatives of Diplomonads and should be excluded from this genus.
Carpediemonas-like organisms (CLOs) comprise a few species of small, free-living Fornicata. They are typical excavates and are biflagellated, though usually possess three or four basal bodies in the mastigont.
CLOs form a paraphyletic grade in phylogenetic trees, having retortamonads, diplomonads, and Caviomonadidae (i.e., the rest of Fornicata) nested within them. Caviomonadidae is a group of morphologically reduced uniflagellates that were thought to belong to Diplomonadida until recently.