''Tunicaraptor'' is a genus of marine

microbial A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s containing the single species ''Tunicaraptor unikontum'', discovered in 2020 from marine waters of

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

. It is a lineage of predatorial

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 the ...

s closely related to animals. It has a rare feeding structure not seen in other opisthokonts.

Morphology

''Tunicaraptor unikontum'' is a small

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 composed of oval

cell Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a de ...

s similar to some

fungal A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as one of the tradit ...

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...

s, with a length of 3–5

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

. It has one

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 ...

with a flagellar pocket, and an external envelope or ‘

theca In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...

’ with long hairs of around 110 nm. Unlike other unicellular

opisthokont The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...

s, ''Tunicaraptor'' cells possess a ‘mouth’, a specialized feeding structure in 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 ...

part of the

. There are two

centriole In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers ( Pinophyta), flowering plants ( angiosperms) and most fungi, an ...

s: one develops a flagellum and the other rotates to the

kinetosome A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor Wi ...

. The

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

crista A crista (; : cristae) is a fold in the inner mitochondrial membrane, inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large a ...

e are flat and associated with

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

globules.

Discovery and etymology

''Tunicaraptor unikontum'' was isolated from marine waters of the coast of

. Its morphology and phylogenetic relationships were analyzed and published in 2020 in the

journal A journal, from the Old French ''journal'' (meaning "daily"), may refer to: *Bullet journal, a method of personal organization *Diary, a record of personal secretive thoughts and as open book to personal therapy or used to feel connected to onesel ...

Current Biology ''Current Biology'' is a biweekly peer-reviewed scientific journal that covers all areas of biology, especially molecular biology, cell biology, genetics, neurobiology, ecology, and evolutionary biology. The journal includes research artic ...

''. The name ''Tunicaraptor'' means ‘predator covered with tunica’, while ''unikontum'' () means ‘single

’.

Ecology

''Tunicaraptor unikontum'' is found in marine environments. It is a eukaryovorous predator, meaning it can only feed on other

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, and it is not capable of consuming

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

. During feeding, many different cells can aggregate and feed jointly on the same eukaryotic prey.

Evolution

''Tunicaraptor'' is an independent lineage of

Holozoa Holozoa () is a clade of organisms that includes animals and their closest single-celled relatives, but excludes fungi and all other organisms. Together they amount to more than 1.5 million species of purely heterotrophic organisms, including a ...

n protists, but its placement is not resolved. Three different phylogenetic positions of ''Tunicaraptor'' have been obtained from analyses: as sister to

Filasterea Filasterea is a proposed basal Filozoan clade of single-celled ameboid eukaryotes that includes '' Ministeria'' and '' Capsaspora''. It is a sister clade to the Choanozoa in which the Choanoflagellatea and Animals appeared, originally proposed b ...

, as sister to

Filozoa The Filozoa are a monophyletic grouping within the Opisthokonta. They include animals and their nearest unicellular relatives (organisms which are more closely related to animals than to fungi or Mesomycetozoa). Three groups are currently inc ...

or as the sister group to all Holozoa. The characteristics of the Rel homology region of the

filasterea Filasterea is a proposed basal Filozoan clade of single-celled ameboid eukaryotes that includes '' Ministeria'' and '' Capsaspora''. It is a sister clade to the Choanozoa in which the Choanoflagellatea and Animals appeared, originally proposed b ...

n '' Txikispora philomaios'' was highly similar to ''Tunicaraptor unikontum'', suggesting a

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

relationship between the two species. In search for the

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s responsible for

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

multicellularity A multicellular organism is an organism that consists of more than one cell, unlike unicellular organisms. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and pa ...

across the eukaryote evolution, a precursor for a

neuropeptide Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

gene, nesfatin-1, has also been found in ''Tunicaraptor unikontum''. These discoveries suggest that neuropeptide signaling in animals has a deep evolutionary ancestry in their unicellular relatives.

References

{{taxonbar, from1=Q118899431, from2=Q122920446 Holozoa Taxa described in 2020 Opisthokont genera Protist genera