Viridiraptoridae, previously known as clade X, is a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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 ...

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...

s in the phylum

Cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eu ...

. They're a family of glissomonads, a group containing a vast, mostly undescribed diversity of

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

and

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

organisms.

Morphology and behavior

Members of Viridiraptoridae 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 ...

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...

s with naked cells, mostly rigid and variously shaped, without any rostrum or bulge. During the life cycle they can present two different states: a large flagellate state for moving, capable of changing into a surface-attached amoeboid state for feeding. The flagellate state exceeds 10 μm, unlike most known glissomonad families. The amoeboid state retains

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

and shows a bridge-like morphology, with several different adhesion sites. Each cell contains a single vesicular

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

close to flagellar apparatus, and has an apical position in the flagellate state. The

nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis, which is the synthesis of ribosomes. The nucleolus also participates in the formation of sig ...

is spherical, roughly central, occasionally showing

lacuna Lacuna (plural lacunas or lacunae) may refer to: Related to the meaning "gap" * Lacuna (manuscripts), a gap in a manuscript, inscription, text, painting, or musical work **Great Lacuna, a lacuna of eight leaves where there was heroic Old Norse po ...

e. The Golgi dictyosomes are close to the

nuclear envelope The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material. The nuclear envelope consists of two lipid bilayer membrane ...

. The

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

is colourless, or opaque due to the presence of globules, granules and crystals inside of it. The feeding stages are seen containing several globules of certain refractivity. The crystal-like structures are restricted to starving cells and are observed in various shapes: #Small, spherical or slightly elongate, glistening particles, between 0.5 and 1 μm. #Slender, fusiform or needle-like rods, often 2 to 3 μm in length, rarely up to around 6 μm. There are several mitochondria scattered throughout cell, slightly elongate. There are spherical

extrusome Extrusomes are membrane-bound structures in some eukaryotes which, under certain conditions, discharge their contents outside the cell. There are a variety of different types, probably not homologous, and serving various functions. Notable extru ...

s, around 0.5 μm in diameter, directly beneath plasma membrane, but not seen in the

pseudopodia A pseudopod or pseudopodium (plural: 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 filament ...

. Several contractile vacuoles appear in the periphery, measuring usually less than 2 μm in diameter. The flagella are naked, heterodynamic (= with different movement each), and arise very close to each other in a slightly acute angle or a right angle. The cells

glide Glide may refer to: * Gliding flight, to fly without thrust Computing *Glide API, a 3D graphics interface *Glide OS, a web desktop *Glide (software), an instant video messenger *Glide, a molecular docking software by Schrödinger (company), Schr� ...

only on their posterior flagellum, which is mostly longer than the anterior flagellum. While gliding, the cell body does not attach to the substrate. The flapping motion of the anterior flagellum often causes motions of the cell body while gliding (such as rotating, jiggling or vibrating). The cells can perform a fluttering swimming locomotion to some extent; this involves both flagella.

Ecology

Viridiraptoridae are

protists that feed by

phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

on live and dead eukaryotic cells. They are capable of degrading the

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

of their prey to feed exclusively on the

protoplast Protoplast (), is a biological term coined by Hanstein in 1880 to refer to the entire cell, excluding the cell wall. Protoplasts can be generated by stripping the cell wall from plant, bacterial, or fungal cells by mechanical, chemical or enzy ...

material (as seen in certain

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 ...

; see image). They are not

bacterivorous A bacterivore is an organism which obtains energy and nutrients primarily or entirely from the consumption of bacteria. The term is most commonly used to describe free-living, heterotrophic, microscopic organisms such as nematodes as well as many s ...

. They propagate by

binary fission Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that t ...

. No plasmodia have been observed. They inhabit

-fed ecosystems.

Classification

Two

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

, both

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

(with one species each), comprise the family: *'' Orciraptor'' **'' Orciraptor agilis'' *''

Viridiraptor ''Viridiraptor'' is a genus of heterotrophic protists, containing the single species ''Viridiraptor invadens''. It belongs to the family Viridiraptoridae, in the phylum Cercozoa. Morphology ''Viridiraptor'' are unicellular biflagellated organism ...

'' **'' Viridiraptor invadens''

References

{{Reflist, refs= {{cite journal, vauthors=Hess S, Melkonian M, title=The Mystery of Clade X: Orciraptor gen. nov. and Viridiraptor gen. nov. are Highly Specialised, Algivorous Amoeboflagellates (Glissomonadida, Cercozoa), journal=Protist, volume=164, issue=5, date=2013, pages=706–747, issn=1434-4610, doi=10.1016/j.protis.2013.07.003 {{cite journal, title=Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria, first1=Thomas, last1=Cavalier-Smith, first2=Ema E., last2=Chao, first3=Rhodri, last3=Lewis, date=April 2018, journal=Protoplasma, volume=255, issue=5 , pages=1517–1574, doi=10.1007/s00709-018-1241-1, pmid=29666938, pmc=6133090 {{cite journal, vauthors=Howe AT, Bass D, Chao EE, Cavalier-Smith T, title=New Genera, Species, and Improved Phylogeny of Glissomonadida (Cercozoa), journal=Protist, volume=162, issue=5, date=2011, pages=710–722, issn=1434-4610, doi=10.1016/j.protis.2011.06.002 {{cite journal, vauthors=Moye J, Schenk T, Hess S, title=Experimental evidence for enzymatic cell wall dissolution in a microbial protoplast feeder (Orciraptor agilis, Viridiraptoridae), journal=BMC Biol, volume=20, pages=267, date=2022, doi=10.1186/s12915-022-01478-x Cercozoa families Taxa described in 2013