Ciliate

Ciliate

Overview
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia
Cilium
A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....

, which are identical in structure to flagella
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...

 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 sessile ciliates which feed by extracellular digestion and lack cilia in the adult phase. They were originally thought to feed by suction – hence their name. In fact, they use specialized microtubules to ensnare and manipulate their prey...

 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
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

.
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Encyclopedia
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia
Cilium
A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....

, which are identical in structure to flagella
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...

 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 sessile ciliates which feed by extracellular digestion and lack cilia in the adult phase. They were originally thought to feed by suction – hence their name. In fact, they use specialized microtubules to ensnare and manipulate their prey...

 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
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

. Ciliophora can be classified under Protista or Protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

. The term "Ciliata" is also used, as a class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

. (However, this latter term can also refer to a type of fish
Fivebeard rockling
The fivebeard rockling is a coastal fish of the Lotidae family. Its body is elongated and up to long. It lives in shallow water on muddy and sandy seafloors, sometimes in the littoral zone...

.) Protista classification is rapidly evolving, and it is not rare to encounter these terms used to describe other hierarchical levels.

Ciliates are one of the most important groups of protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...

s, common almost everywhere there is water — in lakes, ponds, oceans, rivers, and soils. Ciliates have many ectosymbiotic
Ectosymbiosis
Ectosymbiosis is symbiosis in which the symbiont lives on the body surface of the host, including internal surfaces such as the lining of the digestive tube and the ducts of glands....

 and endosymbiotic members, as well as some obligate and opportunistic parasites. Ciliates tend to be large protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

, a few reach 2 mm in length, and are some of the most complex protozoans in structure.

Cell structure


Unlike most other eukaryotes, ciliates have two different sorts of nuclei
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

: a small, diploid micronucleus
Micronucleus
A the micronucleus is the smaller nucleus in ciliate protozoans, such as the paramecium. In fission it divides by mitosis, and in 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...

 (reproduction), and a large, polyploid macronucleus
Macronucleus
A macronucleus is the larger type of 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. Here two cells line up, the micronuclei undergo meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....

, some of the haploid daughters are exchanged and then fuse to form new micronuclei and macronuclei.

Food vacuole
Vacuole
A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain...

s are formed through phagocytosis 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 the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 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 , also known as 'The peni-cytosis', is the durable process by which a cell directs the contents of secretory vesicles out 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, which involve two cells. After conjugation, the two cells divide, forming four new cells.

Specialized structures in ciliates


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. There may also be...

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 a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...

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 , a thin layer supporting the cell membrane in various protozoa*Pellicle mirror, a thin plastic membrane which may be used as a beam splitter or protective cover in optical systems...

 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 eukaryotic cells. These organelles range from 0.5 to 1.0 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, most of which possess a unique organelle called apicoplast and an apical complex structure involved in penetrating a host's cell. They are unicellular, spore-forming, and exclusively parasites of animals. Motile structures such as flagella or...

, 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 temperature, salinity, or depth...

s. These superficially dissimilar groups make up the alveolate
Alveolate
The alveolates are a major line of protists.-Phyla:There are four phyla, which are very divergent in form, but are now known to be close relatives based on various ultrastructural and genetic similarities:...

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. Although appearing as early as the Ordovician period, tintinnids became abundant in the fossil record during the...

s from the Ordovician
Ordovician
The Ordovician is a geologic period and system, 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 . It follows the Cambrian Period and is followed by the Silurian Period...

 Period. In 2007, Li et al. published a description of fossil ciliates from the Doushantuo Formation
Doushantuo Formation
The Doushantuo Formation is a Lagerstätte 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 , named after the Ediacara Hills of South Australia, 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
Suctoria are sessile ciliates which feed by extracellular digestion and lack cilia in the adult phase. They were originally thought to feed by suction – hence their name. In fact, they use specialized microtubules to ensnare and manipulate their prey...

n.

Gene Scrambling


Ciliates are unicellular eukaryotes with two types of nuclei: the somatic “micronucleus” and the germline “macronucleus”. In ciliates, segments of the parental micronuclear gene rearrange in a random order. This concept, known as gene scrambling, occurs when the germline micronuclear genome develops into the somatic macronuclear genome. Segments arrange themselves through various mutations in the gene, such as deletions, duplications, inversions
Inversions
Inversions is a science fiction novel by Scottish writer Iain M. Banks, first published in 1998. It is implied to be set in his Culture universe...

, and translocations.
During the gene scrambling process, genes in the micronuclear genome of ciliates are interrupted by sequences called internal eliminated sequences (IESs). As the micronucleus develops into a somatic nucleus, IESs are excised from the germline gene. The remaining gene segments, called Macronuclear Destined Segments (MDS), are spliced and together and make an operational gene. In this process, the MDSs are often scrambled in an order and orientation relative to the macronuclear copy of the gene for reasons unknown. Each macronuclear segment can be recognized and traced in this gene scrambling process as they are tagged with distinct key sequences.

The study of gene scrambling in ciliate micronucleus genes ties back to the phylogenetic tree
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...

.

Subphylum Postciliodesmatophora

  • Class Karyorelictea
    Karyorelictea
    All ciliate possess multiple dimorphic nuclei which have separated the functions of protein synthesis, preformed by the macronuclei or somatic-nuclei, and heritable DNA replication, performed by the micronuclei or germ-line nuclei...

  • 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. Many species are highly contractile, and are typically compressed or conical in form...

    ea (e.g. Stentor)

Subphylum Intramacronucleata


  • 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. There may also be...

    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. The body cilia are reduced to a girdle and ventral cilia...

      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. Most...

      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. They can also be found swimming on/through decaying vegetation and pond scum floating through the water...

      )
    • 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. Some also have dorsal cilia, which function as sensory bristles. Euplotes and Aspidisca...

      ia (e.g. Euplotes)

  • Class Litostomatea
    Litostomatea
    The Litostomatea are a class of ciliate protists. Until recently, the class Litostomatea was divided into two groups, the Haptoria and the Trichostomatia. However, new genetic information has resulted in the resurrection of a third subclass, Rhynchostomatia, first proposed by A. W. Jankowski in...

    • Subclass Haptoria (e.g. Didinium
      Didinium
      Didinium is a genus of ciliophora. They are free-living carnivores, mostly found in fresh and brackish water environments, although at least three marine species are known. Their diet consists primarily of Paramecium, but some species such as D...

      )
    • 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 (e.g Chilodonella uncinata
      Chilodonella uncinata
      Childonella uncinata is a single-celled organism of the Ciliate class of Protists. As a ciliate, C. uncinata has cilia covering its body and a dual nuclear structure, the micronucleus and macronucleus. Unlike some other ciliates, C...

    • Subclass Rhynchodia
      Rhynchodia
      Rhynchodia is a genus of moths of the Noctuidae family.-References:*...

    • Subclass Chonotrich
      Chonotrich
      Chonotrichia is a subclass of phyllopharyngeid ciliates. These single-celled organisms are sessile at maturity and usually live on crustaceans as ectosymbionts....

      ia
    • Subclass Suctoria
      Suctoria
      Suctoria are sessile ciliates which feed by extracellular digestion and lack cilia in the adult phase. They were originally thought to feed by suction – hence their name. In fact, they use specialized microtubules to ensnare and manipulate their prey...

       (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...

  • Class Colpodea
    Colpodea
    The Colpodea are a class of ciliates, of about 200 species 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. The mouth may be apical or ventral, with more or less prominent...

     (e.g. Colpoda
    Colpoda
    right|thumb|250px|Typical large colpoda @ 400Xright|thumb|250px|Measurements of large colpoda in micrometresColpoda is a genus of ciliate in the class Colpodea Order Colpodida Family Colpodidae.- Description :...

    )
  • Class Prostomatea
    Prostomatea
    Prostomatea is a class of Ciliophora. It includes the genera Coleps and Pelagothrix....

     (e.g. Coleps
    Coleps
    It is a cell.Coleps is a genus of ciliated Prostomatea with barrel-shaped bodies. The can grow up to 250 micrometers in length, but are usually under 100 micrometers in their longest axis. Coleps can be taxonomically distinguished by the ornamentation of their ectoplasmic calcium carbonate...

    )
  • 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. These include a paroral membrane to the right of the mouth and membranelles, usually three in number, to its left. The...

    • 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. They have simple life cycles, and in many cases do not even form resting cysts.Typically...

       (e.g. Paramecium
      Paramecium
      Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 0.05 to 0.35 mm in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion at speeds of approximately 12 body...

      )
    • 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. Among these is the important species Ichthyopthirius multifiliis, a common cause of death in aquaria and...

       (e.g. Tetrahymena
      Tetrahymena
      Tetrahymena are free-living ciliate protozoa that can also switch from commensalistic to pathogenic modes of survival. They are common in fresh-water. Tetrahymena species used as model organisms in biomedical research are T. thermophila and T. pyriformis.- T...

      )
    • 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 membranelles...

      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. Each cell has a separate stalk anchored onto the substrate, which contains a contractile fibril called a myoneme. When stimulated this shortens, causing the...

      )
    • 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...