Thecamonadinae is a subfamily of

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

protists A protist ( ) or protoctist is any Eukaryote, eukaryotic organism that is not an animal, Embryophyte, land plant, or fungus. Protists do not form a Clade, natural group, or clade, but are a Paraphyly, paraphyletic grouping of all descendants o ...

. It is a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group, or

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

, of

apusomonad The apusomonads (family Apusomonadidae) are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts ...

s, a group of

protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...

with two

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

closely related to the eukaryotic supergroup Opisthokonta. The subfamily contains two genera ''

Chelonemonas ''Chelonemonas'' () is a genus of heterotrophic protists. They are unicellular eukaryotes with two flagella, characterized by the presence of a honeycomb or turtle shell pattern on the dorsal surface of their cells that is visible under electron ...

'' and ''

Thecamonas Thecamonadinae is a subfamily of heterotrophic protists. It is a monophyletic group, or clade, of apusomonads, a group of protozoa with two flagella closely related to the eukaryotic supergroup Opisthokonta. The subfamily contains two genera ''Ch ...

'', which are found in marine habitats.

Morphology

Thecamonadinae are

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s, exhibiting cells smaller than 10 μm, and an "''

Amastigomonas ''Amastigomonas'' is a genus of protists belonging to a lineage of biciliated zooflagellates known as Apusomonadida. It was first described in 1931 by Henri de Saedeleer. The current use of ''Amastigomonas'' is as a descriptive archetype, with n ...

''-type" cell body shape: plastic, oval to oblong, with a prominent proboscis that measures around ¼ of the cell body length. They have a rigid "tusk" of between 200 and 250 nm in diameter, that arises to the right of the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

flagellum A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

and extends around 0.5–1.0 μm. This tusk can be visible under optimal conditions of

light microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical, el ...

. Aside from the flagella, they often present thin

pseudopodia A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...

trailing behind the moving cell.

Systematics

History of taxonomy

Thecamonadinae was initially a family-level

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

, Thecamonadidae, described in 1990 by Jacob Larsen and David J. Patterson. At the time, it was composed exclusively of the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

'', described by the same authors. Members of this family were characterized by a mobile anterior "snout" (or "tusk"), which is superficially resembling of the flagellate '' Rhynchomonas''. However, their

ultrastructure Ultrastructure (or ultra-structure) is the architecture of cells and biomaterials that is visible at higher magnifications than found on a standard optical light microscope. This traditionally meant the resolution and magnification range of a c ...

resembled ''

Apusomonas ''Apusomonas'' is a genus of Apusozoa The Apusozoa are a paraphyletic phylum of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together ...

'' in the pliable dorsal theca. Posterior phylogenetic analyses showed that this family branched within

Apusomonadidae The apusomonads (family Apusomonadidae) are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts, ...

, and the taxon fell out of use. In 2015, Aaron A. Heiss and collaborators co-opted this taxon as a subfamily within

to designate the

uniting ''

'' and ''

''. This clade is supported by multiple

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

and accepted as a valid taxon.

Classification

As of 2022, the subfamily contains two genera, ''

'' and ''

'', and a total of 7 species. *''

'' :*'' C. dolani'' :*'' C. geobuk'' :*'' C. masanensis'' *''

'' :*'' T. filosa'' = ''Amastigomonas filosa'' :*'' T. muscula'' = ''Amastigomonas muscula'' :*'' T. mutabilis'' = ''Rhynchomonas mutabilis'' = ''Amastigomonas mutabilis'' :*'' T. trahens'' = ''Amastigomonas trahens''

References

{{Taxonbar, from=Q123003427 Taxa described in 1990 Apusomonadida