''Pseudoblepharisma'' is a genus of

heterotrich The heterotrichs are a class of ciliates. They typically have a prominent adoral zone of membranelles circling the mouth, used in locomotion and feeding, and shorter cilia on the rest of the body. Many species are highly contractile, and are ...

ciliates The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

inhabiting oxygen depleted freshwater habitats. Most sources report that it contains one species, ''Pseudoblepharisma tenue'', but at least four have been seen in literature. ''P. tenue'' was originally described in Germany as ''Blepharisma tenuis''. Starting in 2006, it was recognized that the German strain may have two bacterial symbionts, one pink, one green. In 2021, both symbionts were confirmed to be photosynthetic: a ''

Chlorella ''Chlorella'' is a genus of about thirteen species of single-celled green algae belonging to the division Chlorophyta. The cells are spherical in shape, about 2 to 10 μm in diameter, and are without flagella. Their chloroplasts contain the ...

'' sp. K10 (

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

), discovered earlier as a symbiont of ''

Hydra viridissima ''Hydra viridissima'' is a species of cnidarian which is commonly found in still or slow-moving freshwater in the Northern temperate zone. ''Hydra viridissima'' is commonly called green hydra due to its coloration, which is due to the symbiotic ...

''; and Ca. '' Thiodictyon intracellulare'' (

Chromatiaceae The Chromatiaceae are one of the two families of purple sulfur bacteria, together with the Ectothiorhodospiraceae. They belong to the order Chromatiales of the class Gammaproteobacteria, which is composed by unicellular Gram-negative organisms. ...

), a purple sulfur bacterium that has lost its sulfur-metabolizing genes. The complexity of such a tripartite symbiosis is novel to science. European reports also mentioned a variant ''P. tenue'' var. ''viride'', which only has green symbionts. In 2022, one strain matching these descriptions was found in tropical freshwaters of

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, North America. Unlike its the bicolor European counterpart, it builds a lorica (shell) around itself. The current taxonomy is inconsistent with molecular phylogeny using

SSU rRNA Small subunit ribosomal ribonucleic acid (SSU rRNA) is the smaller of the two major RNA components of the ribosome. Associated with a number of ribosomal proteins, the SSU rRNA forms the small subunit of the ribosome. It is encoded by SSU- rDNA. ...

; the latter places the genus sister to ''

Spirostomum ''Spirostomum'' is a genus of ciliated protists that belongs to the class Heterotrichea. It is known for being very contractile.Fernandes, N.M.; da Silva Neto, I.D. (2013). “Morphology and 18S rDNA gene sequence of ''Spirostomum minus'' and ''S ...

''.

References

{{reflist Heterotrichea Alveolata genera