The suffix -monas is used in microbiology for many genera and is intended to mean "unicellular organism".

Meaning

The suffix -monas is used in microbiology for many genera in a similar way to -bacter

-bacter

-Meaning:Bacter is a Neolatin term coined from bacterium, which in turn derives from the Greek βακτήριον, meaning small staff...

, -bacillus

Bacillus (shape)

The word bacillus may be used to describe any rod-shaped bacterium, and such bacilli are found in many different taxonomic groups of bacteria. However, the name Bacillus, capitalized and italicized, refers to a specific genus of bacteria...

, -coccus

Coccus

Coccus can be used to describe any bacterium that has a spherical shape. It is one of the three distinct types of bacteria shapes, the other two being bacillus and spirillum cells...

 or -spirillum

Spirillum

Spirillum in microbiology refers to a bacterium with a cell body that twists like a spiral. It is the third distinct bacterial cell shape type besides coccus and bacillus cells.-Taxonomic:...

. The genera with the suffix monas are not a monophyletic group and the suffix is chosen over -bacter, often simply out of stylistic preferences to match with Greek words.

The first genus to be given the suffix -monas was the Pseudomonas

Pseudomonas

Pseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...

, a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of gammaproteobacteria

Gammaproteobacteria

Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria, such as the Enterobacteriaceae , Vibrionaceae and Pseudomonadaceae. An exceeding number of important pathogens belongs to this class, e.g...

. The generic epithet Pseudomonas was coined by Walter Migula

Walter Migula

Walter Emil Friedrich August Migula was a German botanist, who published many articles on the subjects of cryptogamic botany, bacteriology, and plant physiology...

 in 1894, who did not give an etymology.
Since the 7th edition of Bergey's manual (=top authority in bacterial nomeclature), other authors have given the etymology to be: Greek

Ancient Greek

Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 pseudes (ψευδες) (false) and monas (μονάς / μονάδα a single unit), which can mean "false unit". However, "false unit" conceptually does not make much sense, namely, it does not mean "an organism which may falsely appear as a single unit but it is not" as it is not found in multicellular chains nor was it ever described as such. One speculation is that the name was chosen simply out of aesthetics,while the most plausible theory states that Migula intended it as false Monas, a nanoflagellate protist (Chrysophyceae: Ochromonadales: Ochromonadaceae: Chrysomonadida: Ochromonadidae). Subsequently, the term "monas" was used in the early history of microbiology to denote single-celled organisms.

Grammar

When suffices are added to a name of a genus ending in -monas to make higher ranks, the stem becomes -monad-, in fact it is quite common in Greek and in Latin that the stem differs between the singular nominative case and the rest (c.f. Latin declension

Latin declension

Latin is an inflected language, and as such has nouns, pronouns, and adjectives that must be declined in order to serve a grammatical function. A set of declined forms of the same word pattern is called a declension. There are five declensions, which are numbered and grouped by ending and...

 or Greek declension), here μονάς / μονάδα.

In English to make a vernacular name for members of a genus, i.e. trivialising the scientific name, the scientific name is taken and written with sentence case and in roman type (i.e. "standard") as opposed to uppercase italic, the plurals are generally constructed by adding an "s", regardless of Greco-Roman grammar. In the case of genera ending in monas the ending is changed to monad with plural -monads. Example: a member of the Pseudomonas genus is a pseudomonad, while two are pseudomonads. The use of the stem for non-nominative cases is seen more often in botany, where trivialisation is more common, e.g. a bromeliad is a member of the genus Bromelia

Bromelia

Bromelia is a genus of the botanical family Bromeliaceae, subfamily Bromelioideae. Bromelia species are characterized by flowers with a deeply cleft calyx. The genus is named after the Swedish medical doctor and botanist Olaf Bromelius .-Species:* Bromelia agavifolia Brongniart ex Houllet*...

.

Archeal genera

Genus	Phylum	Order	Class	Family
Natronomonas	Euryarchaeota	Halobacteria	Halobacteriales	Halobacteriaceae
Thermogymnomonas	Euryarchaeota	Thermoplasmata	Thermoplasmatales

Bacterial genera

Genus	Phylum	Order	Class	Family
Acidomonas	Proteobacteria	Alphaproteobacteria	Rhodospirillales	Acetobacteraceae
Aeromonas	Proteobacteria	Gammaproteobacteria	Aeromonadales	Aeromonadaceae
Agromonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Bradyrhizobiaceae
Aidingimonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Halomonadaceae
Albimonas	Proteobacteria	Alphaproteobacteria	Rhodobacterales	Rhodobacteraceae
Alkalimonas	Proteobacteria	Gammaproteobacteria
Allomonas	Proteobacteria	Gammaproteobacteria	Vibrionales	Vibrionaceae
Alteromonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Alteromonadaceae
Aminomonas	Synergistetes	Synergistia	Synergistales	Synergistaceae
Aquimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Aquisalimonas	Proteobacteria	Gammaproteobacteria	Chromatiales	Ectothiorhodospiraceae
Arenimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Arhodomonas	Proteobacteria	Gammaproteobacteria	Chromatiales	Ectothiorhodospiraceae
Aspromonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Aurantimonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Aurantimonadaceae
Azohydromonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Alcaligenaceae
Azomonas	Proteobacteria	Gammaproteobacteria	Pseudomonadales	Pseudomonadaceae
Balneimonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Bradyrhizobiaceae
Blastomonas	Proteobacteria	Alphaproteobacteria	Sphingomonadales	Sphingomonadaceae
Brachymonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Brevundimonas	Proteobacteria	Alphaproteobacteria	Caulobacterales	Caulobacteraceae
Butyricimonas	Bacteroidetes	Bacteroidia	Bacteroidales	Porphyromonadaceae
Caenimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Caldimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Camelimonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Beijerinckiaceae
Carnimonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Halomonadaceae
Celerinatantimonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Celerinatantimonadaceae
Cellulomonas	Actinobacteria	Actinobacteria	Actinomycetales	Cellulomonadaceae
Chitinimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Burkholderiaceae
Chryseomonas	Proteobacteria	Gammaproteobacteria	Pseudomonadales	Pseudomonadaceae
Citreimonas	Proteobacteria	Alphaproteobacteria	Rhodobacterales	Rhodobacteraceae
Cocleimonas	Proteobacteria	Gammaproteobacteria
Collimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Oxalobacteraceae
Comamonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Conglomeromonas	Proteobacteria	Alphaproteobacteria	Rhodospirillales	Rhodospirillaceae
Dechloromonas	Proteobacteria	Betaproteobacteria	Rhodocyclales	Rhodocyclaceae
Dehalogenimonas	Chloroflexi	Dehalococcoidetes
Desulfomonas	Proteobacteria	Deltaproteobacteria	Desulfovibrionales	Desulfovibrionaceae
Desulfosalsimonas	Proteobacteria	Deltaproteobacteria	Desulfobacterales	Desulfobacteraceae
Desulfuromonas	Proteobacteria	Deltaproteobacteria	Desulfuromonadales	Desulfuromonadaceae
Dysgonomonas	Bacteroidetes	Bacteroidia	Bacteroidales	Porphyromonadaceae
Endozoicomonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Hahellaceae
Epilithonimonas	Bacteroidetes	Flavobacteria	Flavobacteriales	Flavobacteriaceae
Erythromonas	Proteobacteria	Alphaproteobacteria	Sphingomonadales	Sphingomonadaceae
Ferrimonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Ferrimonadaceae
Filimonas	Bacteroidetes	Sphingobacteria	Sphingobacteriales	Chitinophagaceae
Flagellimonas	Bacteroidetes	Flavobacteria	Flavobacteriales	Flavobacteriaceae
Flavimonas	Proteobacteria	Gammaproteobacteria	Pseudomonadales	Pseudomonadaceae
Fulvimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Gallaecimonas	Proteobacteria	Gammaproteobacteria
Gemmatimonas	Gemmatimonadetes	Gemmatimonadetes	Gemmatimonadales	Gemmatimonadaceae
Gracilimonas	Bacteroidetes	Sphingobacteria	Sphingobacteriales	Chitinophagaceae
Halomonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Halomonadaceae
Herminiimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Oxalobacteraceae
Hydrogenimonas	Proteobacteria	Epsilonproteobacteria	Campylobacterales	Hydrogenimonaceae
Hyphomonas	Proteobacteria	Alphaproteobacteria	Caulobacterales	Hyphomonadaceae
Kistimonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Hahellaceae
Kordiimonas	Proteobacteria	Alphaproteobacteria	Kordiimonadales	Kordiimonadaceae
Lebetimonas	Proteobacteria	Epsilonproteobacteria	Nautiliales	Nautiliaceae
Luteimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Lutimonas	Bacteroidetes	Flavobacteria	Flavobacteriales	Flavobacteriaceae
Macromonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Malonomonas	Proteobacteria	Deltaproteobacteria	Desulfuromonadales	Desulfuromonadaceae
Marinomonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Oceanospirillaceae
Maritimimonas	Bacteroidetes	Flavobacteria	Flavobacteriales	Flavobacteriaceae
Marixanthomonas	Bacteroidetes	Flavobacteria	Flavobacteriales	Flavobacteriaceae
Megamonas	Firmicutes	Negativicutes	Selenomonadales	Veillonellaceae
Methylohalomonas	Proteobacteria	Gammaproteobacteria
Methylomonas	Proteobacteria	Gammaproteobacteria	Methylococcales	Methylococcaceae
Miniimonas	Actinobacteria	Actinobacteria	Actinomycetales	Beutenbergiaceae
Neptunomonas	Proteobacteria	Gammaproteobacteria	Oceanospirillales	Oceanospirillaceae
Nitrosomonas	Proteobacteria	Betaproteobacteria	Nitrosomonadales	Nitrosomonadaceae
Oceanimonas	Proteobacteria	Gammaproteobacteria	Aeromonadales	Aeromonadaceae
Paraferrimonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Ferrimonadaceae
Parapusillimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Alcaligenaceae
Parvimonas	Firmicutes	Clostridia	Clostridiales
Paucimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Burkholderiaceae
Pelomonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Petrimonas	Bacteroidetes	Bacteroidia	Bacteroidales	Porphyromonadaceae
Pleomorphomonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Methylocystaceae
Plesiomonas	Proteobacteria	Gammaproteobacteria	Enterobacteriales	Enterobacteriaceae
Polaromonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Comamonadaceae
Porphyromonas	Bacteroidetes	Bacteroidia	Bacteroidales	Porphyromonadaceae
Propionicimonas	Actinobacteria	Actinobacteria	Actinomycetales	Propionibacteriaceae
Protomonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Methylobacteriaceae
Pseudoalteromonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Pseudoalteromonadaceae
Pseudofulvimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Pseudomonas	Proteobacteria	Gammaproteobacteria	Pseudomonadales	Pseudomonadaceae
Pseudoxanthomonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Psychromonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Psychromonadaceae
Pusillimonas	Proteobacteria	Betaproteobacteria	Burkholderiales	Alcaligenaceae
Rhizomonas	Proteobacteria	Alphaproteobacteria	Sphingomonadales	Sphingomonadaceae
Rhodopseudomonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Bradyrhizobiaceae
Roseomonas	Proteobacteria	Alphaproteobacteria	Rhodospirillales	Acetobacteraceae
Rubrimonas	Proteobacteria	Alphaproteobacteria	Rhodobacterales	Rhodobacteraceae
Rugamonas	Proteobacteria	Gammaproteobacteria	Pseudomonadales	Pseudomonadaceae
Salinarimonas	Proteobacteria	Alphaproteobacteria	Rhizobiales	Bradyrhizobiaceae
Salinimonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Alteromonadaceae
Sediminimonas	Proteobacteria	Alphaproteobacteria	Rhodobacterales	Rhodobacteraceae
Selenomonas	Firmicutes	Negativicutes	Selenomonadales	Veillonellaceae
Silanimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Silvimonas	Proteobacteria	Betaproteobacteria	Neisseriales	Neisseriaceae
Singularimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Sinobacteraceae
Sinomonas	Actinobacteria	Actinobacteria	Actinomycetales	Micrococcaceae
Solimonas	Proteobacteria	Gammaproteobacteria
Sphingomonas	Proteobacteria	Alphaproteobacteria	Sphingomonadales	Sphingomonadaceae
Stenotrophomonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Succinatimonas	Proteobacteria	Gammaproteobacteria	Aeromonadales	Succinivibrionaceae
Succinimonas	Proteobacteria	Gammaproteobacteria	Aeromonadales	Succinivibrionaceae
Sulfurimonas	Proteobacteria	Epsilonproteobacteria	Campylobacterales	Helicobacteraceae
Syntrophomonas	Firmicutes	Clostridia	Clostridiales	Syntrophomonadaceae
Tepidimonas	Proteobacteria	Betaproteobacteria	Burkholderiales
Terrimonas	Bacteroidetes	Sphingobacteria	Sphingobacteriales	Chitinophagaceae
Thalassomonas	Proteobacteria	Gammaproteobacteria	Alteromonadales	Colwelliaceae
Thermanaeromonas	Firmicutes	Clostridia	Thermoanaerobacterales	Thermoanaerobacteraceae
Thermomonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Thiohalomonas	Proteobacteria	Gammaproteobacteria
Thiomonas	Proteobacteria	Betaproteobacteria	Burkholderiales
Tolumonas	Proteobacteria	Gammaproteobacteria	Aeromonadales	Aeromonadaceae
Tranquillimonas	Proteobacteria	Alphaproteobacteria	Rhodobacterales	Rhodobacteraceae
Tropicimonas	Proteobacteria	Alphaproteobacteria	Rhodobacterales	Rhodobacteraceae
Wohlfahrtiimonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Xanthomonas	Proteobacteria	Gammaproteobacteria	Xanthomonadales	Xanthomonadaceae
Xylanimonas	Actinobacteria	Actinobacteria	Actinomycetales	Promicromonosporaceae
Zymomonas	Proteobacteria	Alphaproteobacteria	Sphingomonadales	Sphingomonadaceae