Ciliate

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Ciliate

The ciliates are a group of protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s characterized by the presence of hair-like organelles called cilia

Cilium

A cilium is an organelle found in eukaryote cell s. Cilia are tail-like projections extending approximately 5?10 micrometres from the cell body....
, which are identical in structure to flagella

Flagellum

A flagellum is a tail-like structure that projects from the cell body of certain prokaryotic and eukaryotic cells, and it functions in locomotion....
but typically shorter and present in much larger numbers with a different undulating pattern than flagella. Cilia occur in all members of the group (although the peculiar suctoria

Suctoria

Suctoria are peculiar ciliates which are sessile, feed by extracellular digestion and lack cilia in the adult phase. They are found in both freshwater and marine environments, including some which live on the surface of aquatic animals, and typically feed on other ciliates....
only have them for part of the life-cycle) and are variously used in swimming, crawling, attachment, feeding, and sensation.

The term "Ciliophora" is used in classification as a phylum

Phylum

A phylum "Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states. is a taxonomic rank below Kingdom and above Class ....
.

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Cell structure

Unlike other eukaryotes, ciliates have two different sorts of nuclei

Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
: a small, diploid micronucleus

Micronucleus

A micronucleus is the smaller cell nucleus in ciliate protozoans, such as the paramecium. In binary fission it divides by mitosis, and in bacterial conjugation furnishes the pairing of gamete nuclei, by whose reciprocal fusion a zygote nucleus is formed, which gives rise to the macronuclei and micronuclei of the individuals of the next cycle...
(reproduction), and a large, polyploid macronucleus

Macronucleus

A macronucleus is the larger type of cell nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, the everyday tasks, such as metabolism....
(general cell regulation). The latter is generated from the micronucleus by amplification of the genome and heavy editing. Division of the macronucleus occurs by amitosis, the segregation of the chromosomes is by a process whose mechanism is unknown. This process is by no means perfect, and after about 200 generations the cell shows signs of aging. Periodically the macronuclei must be regenerated from the micronuclei. In most, this occurs during conjugation
Conjugation

Conjugation may refer to:*Grammatical conjugation, the modification of a verb from its basic form, including:**Latin conjugation**Spanish conjugation...
. Here two cells line up, the micronuclei undergo meiosis

Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
, some of the haploid daughters are exchanged and then fuse to form new micronuclei and macronuclei.

Food vacuole

Vacuole

A vacuole is a membrane organelle which is present in all eukaryotic cells. Vacuoles are essentially enclosed compartments which are filled with fluid such as water or various enzymes, though in certain cases they may contain solids which have been engulfed....
s are formed through phagocytosis

Phagocytosis

File:Phagocytosis in three steps.pngPhagocytosis is the cell process of Phagocytes and Protists of engulfing solid particles by the cell membrane to form an internal phagosome, which is a food vacuole, or pteroid....
and typically follow a particular path through the cell as their contents are digested and broken down via lysosomes so the substances the vacuole contains are then small enough to diffuse

Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
through the membrane of the food vacuole into the cell. Anything left in the food vacuole by the time it reaches the cytoproct (anus) is discharged via exocytosis

Exocytosis

Exocytosis is the durable process by which a cell directs the contents of secretory Vesicle_ out of the cell membrane. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane....
. Most ciliates also have one or more prominent contractile vacuoles, which collect water and expel it from the cell to maintain osmotic pressure, or in some function to maintain ionic balance. These often have a distinctive star-shape, with each point being a collecting tube.

Feeding

Most ciliates feed on smaller organisms (heterotrophic), such as bacteria and algae, and detritus swept into the oral groove (mouth) by modified oral cilia. This usually includes a series of membranelles to the left of the mouth and a paroral membrane to its right, both of which arise from polykinetids, groups of many cilia together with associated structures. The food is moved by the cilia through the mouth pore into the gullet, which forms food vacuoles.

This varies considerably, however. Some ciliates are mouthless and feed by absorption, while others are predatory and feed on other protozoa and in particular on other ciliates. This includes the suctoria, which feed through several specialized tentacles.

Reproduction

Ciliates can undergo both asexual and sexual reproduction. Asexual reproduction occurs by binary fission. The micronucleus undergoes by mitosis and the macronucleus elongates and splits in half. Both new cells each obtain a copy of the micronucleus and macronucleus. Sexual reproduction involves conjugation

Conjugation

Conjugation may refer to:*Grammatical conjugation, the modification of a verb from its basic form, including:**Latin conjugation**Spanish conjugation...
, which involve two cells. After conjugation, the two cells divide, forming four new cells.

Specialized structures

In some forms there are also body polykinetids, for instance, among the spirotrich

Spirotrich

The spirotrichs are a large and distinctive group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down to the left side of the mouth....
s where they generally form bristles called cirri. More often body cilia are arranged in mono- and dikinetids, which respectively include one and two kinetosomes (basal bodies), each of which may support a cilium. These are arranged into rows called kineties, which run from the anterior to posterior of the cell. The body and oral kinetids make up the infraciliature, an organization unique to the ciliates and important in their classification, and include various fibrils and microtubule

Microtubule

Microtubules are one of the components of the cytoskeleton. They have a diameter of 25 Nanometre and length varying from 200 nanometers to 25 micrometers....
s involved in coordinating the cilia.

The infraciliature is one of the main component of the cell cortex. Another are the alveoli, small vesicles under the cell membrane that are packed against it to form a pellicle

Pellicle

Pellicle may refer to:*Pellicle , the outermost layer of a mushroom; often used only for a surface that is viscid and easily peels.*Pellicle , a thin layer supporting the cell membrane in various protozoa...
maintaining the cell's shape, which varies from flexible and contractile to rigid. Numerous mitochondria

Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryote cell . These organelles range from 0.5–10 micrometers in diameter....
and extrusome

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....
s are also generally present. The presence of alveoli, the structure of the cilia, the form of mitosis and various other details indicate a close relationship between the ciliates, Apicomplexa

Apicomplexa

The Apicomplexa are a large group of protists, characterized by the presence of a unique organelle called an apical complex . They are unicellular, spore-forming, and exclusively parasites of animals....
, and dinoflagellate

Dinoflagellate

The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on sea surface temperature, salinity, or depth....
s. These superficially dissimilar groups make up the alveolate

Alveolate

The alveolates are a major line of protists....
s.

Fossil record

Until recently, the oldest ciliate fossils known were tintinnid

Tintinnid

Tintinnids are ciliates of the choreotrich taxon Tintinnida, distinguished by vase-shaped shells called loricae, which are mostly protein but may incorporate minute pieces of minerals....
s from the Ordovician

Ordovician

The Ordovician is a geologic period, the second of six of the Paleozoic era , and covers the time between 488.3?1.7 to 443.7?1.5 million years ago ....
Period. In 2010, Li et al. published a description of fossil ciliates from the Doushantuo Formation

Doushantuo Formation

The Doushantuo Formation is a lagerst?tten in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils....
, about 580 million years ago, in the Ediacaran

Ediacaran

The Ediacaran Period is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon....
Period. These included two types of tintinnids and a possible ancestral suctoria

Suctoria

Classification

Phylum Ciliophora

Class Karyorelictea
Class Heterotrich
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....
ea (e.g. Stentor)
* Class Spirotrich
Spirotrich

The spirotrichs are a large and distinctive group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down to the left side of the mouth....
ea

Subclass Choreotrich
Choreotrich

The choreotrichs are a group of small, marine ciliates. Their name reflects the impression that they appear to dance . The group includes the tintinnids, which produce species-specific loricae , and are important because these may be preserved as microfossils....
ia (e.g. Tintinnidium)
Subclass Oligotrich
Oligotrich

The oligotrichs are a group of ciliate protozoa, included among the spirotrichs. They have prominent oral cilia, which are arranged as a collar and lapel, in contrast to the choreotrichs where they form a complete circle....
ia (e.g. Halteria)
Subclass Stichotrich
Stichotrich

The stichotrichs are a group of ciliate protozoa, included among the spirotrichs. Like the hypotrichs, with which they were originally classified, they have body cilia fused into cirri, but these are mostly arranged into rows, running along the ventral surface or edges of the cell....
ia (e.g. Stylonychia
Stylonychia

Stylonychia is a genus of ciliate, included among the stichotrichs. It is very common in fresh water and soil, found on filamentous algae, surface films, and among particles of sediment....
)
Subclass Hypotrich
Hypotrich

The hypotrichs are a group of ciliate protozoa, included among the spirotrichs. Most are oval in shape, with a rigid pellicle, and have cirri distributed in isolated tufts on the ventral surface of the cell....
ia (e.g. Euplotes)

Class Litostomatea
Litostomatea

The Litostomatea are a class of ciliate protozoa, divided into two groups, ranked as subclasses. The Haptoria includes mostly carnivorous forms, for instance Didinium, a species of which preys exclusively on the ciliate Paramecium....

Subclass Haptoria (e.g. Didinium
Didinium

Didinium is a genus of ciliate. They are free-living carnivores, mostly found in fresh and brackish water environments, although at least three marine species are known....
)
Subclass Trichostomatia (e.g. Balantidium)
* Class Phyllopharyngea
Phyllopharyngea

The Phyllopharyngea are a class of ciliate protozoa, including some which are extremely specialized. Motile cells typically have cilia restricted to the ventral surface, or some part thereof, arising from monokinetids with a characteristic ultrastructure....
Subclass Phyllopharyngia
Subclass Rhynchodia
Subclass Chonotrichia
Subclass Suctoria
Suctoria

Suctoria are peculiar ciliates which are sessile, feed by extracellular digestion and lack cilia in the adult phase. They are found in both freshwater and marine environments, including some which live on the surface of aquatic animals, and typically feed on other ciliates....
(e.g. Podophrya)

Class Nassophorea
Nassophorea

The Nassophorea are a class of ciliate protozoa. Members are free-living, usually in freshwater but also in marine and soil environments. The mouth is anterior ventral and leads to a curved cytopharynx supported by a prominent palisade of rods or nematodesmata, forming a structure called a cyrtos or nasse, typical of this and a...
Class Colpodea
Colpodea

.The Colpodea are a class of ciliate protozoa, common in freshwater and soil habitats. The body cilia are typically uniform, and are supported by dikinetids of characteristic structure, with cilia on both kinetosomes....
(e.g. Colpoda)
Class Prostomatea (e.g. Coleps)
Class Oligohymenophorea
Oligohymenophorea

The Oligohymenophorea are a large class of ciliate protozoa. There is typically a ventral groove containing the mouth and distinct oral cilia, separate from those of the body....

Subclass Peniculia
Peniculid

The peniculids are an order of ciliate protozoa, including the well-known Paramecium and its close relatives. Most are relatively large, freshwater forms that feed on smaller organisms swept into the mouth....
(e.g. Paramecium
Paramecium

Paramecia, also known as Lady Slippers, due to their appearance, are a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 50 to 350 micrometre in length, Simple cilia cover the body, which allow the cell to move with a synchronous motion ....
)
Subclass Hymenostomatia
Hymenostome

The hymenostomes are an order of ciliate protozoa. Most are free-living in freshwater, such as the commonly studied genus Tetrahymena, but some are parasitic on fish or aquatic invertebrates....
(e.g. Tetrahymena
Tetrahymena

Tetrahymena are free-living ciliate protozoa that can also switch from commensalism to pathogenic modes of survival. They are common in fresh-water....
)
Subclass Scuticociliatia
Subclass Peritrich
Peritrich

The peritrichs are a large and distinctive group of ciliate protozoa. They are usually bell or disc shaped, with a prominent paroral membrane arising from the oral cavity and circling counter-clockwise around the anterior of the cell, accompanied by a smaller series of biological membrane....
ia (e.g. Vorticella
Vorticella

Vorticella is a genus of protozoa, with over 16 known species. They are stalked inverted bell-shaped ciliates, placed among the peritrichs....
)
Subclass Astromatia
Astome

Astomes are a group of ciliate protozoans commonly found in the guts of annelid worms, especially oligochaetes, and other invertebrates. As their name implies, these parasites are characterized by an absence of mouth....
Subclass Apostomatia

Class Plagiopylea
Plagiopylid

The plagiopylids are a small order of ciliate protozoa, including a few forms common in anaerobic habitats.The body cilia are dense, and arise from monokinetids with an entirely unique ultrastructure; one or two rows of dikinetids run into the oral cavity, which takes the form of a groove, with a deep tube lined by oral cilia leading to the...