The anal pore or cytoproct is a structure in various single-celled eukaryotes where waste is ejected after the nutrients from food have been absorbed into the cytoplasm .
52-595: See text for subclasses. The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia , which are identical in structure to eukaryotic flagella , but are in general 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 only have them for part of their life cycle ) and are variously used in swimming, crawling, attachment, feeding, and sensation. Ciliates are an important group of protists , common almost anywhere there
104-406: A plastid . Chromerids, apicomplexans, and peridinin dinoflagellates have retained this organelle . Going one step even further back, the chromerids, the peridinin dinoflagellates and the heterokont algae have been argued to possess a monophyletic plastid lineage in common, i.e. acquired their plastids from a red alga , and so it seems likely that the common ancestor of alveolates and heterokonts
156-411: A chain of new organisms); and palintomy (multiple fissions, usually within a cyst ). Fission may occur spontaneously, as part of the vegetative cell cycle . Alternatively, it may proceed as a result of self-fertilization ( autogamy ), or it may follow conjugation , a sexual phenomenon in which ciliates of compatible mating types exchange genetic material. While conjugation is sometimes described as
208-487: 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 microtubules involved in coordinating the cilia. In some forms there are also body polykinetids, for instance, among the spirotrichs where they generally form bristles called cirri . The infraciliature
260-533: A close relationship between the ciliates, Apicomplexa , and dinoflagellates . These superficially dissimilar groups make up the alveolates . Most ciliates are heterotrophs , feeding on smaller organisms, 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
312-448: A form of reproduction, it is not directly connected with reproductive processes, and does not directly result in an increase in the number of individual ciliates or their progeny. Ciliate conjugation is a sexual phenomenon that results in genetic recombination and nuclear reorganization within the cell. During conjugation, two ciliates of a compatible mating type form a bridge between their cytoplasms . The micronuclei undergo meiosis ,
364-538: A leech cocoon from the Triassic period , about 200 million years ago. According to the 2016 phylogenetic analysis, Mesodiniea is consistently found as the sister group to all other ciliates. Additionally, two big sub-groups are distinguished inside subphylum Intramacronucleata : SAL ( Spirotrichea + Armophorea + Litostomatea ) and CONthreeP or Ventrata ( Colpodea + Oligohymenophorea + Nassophorea + Phyllopharyngea + Plagiopylea + Prostomatea ). The class Protocruziea
416-475: A model alveolate, having been genetically studied in great depth over the longest period of any alveolate lineage. They are unusual among eukaryotes in that reproduction involves a micronucleus and a macronucleus . Their reproduction is easily studied in the lab, and made them a model eukaryote historically. Being entirely predatory and lacking any remnant plastid, their development as a phylum illustrates how predation and autotrophy are in dynamic balance and that
468-407: A new macronucleus is generated from the post-conjugal micronucleus. Food vacuoles are formed through phagocytosis and typically follow a particular path through the cell as their contents are digested and broken down by lysosomes so the substances the vacuole contains are then small enough to diffuse through the membrane of the food vacuole into the cell. Anything left in the food vacuole by
520-411: A pair of small anal pores located adjacent to the apical sensory organ which is thought to control osmotic pressure. These animals are also with animal pore. Ctenophores have sometimes been interpreted as homologous with the anus of bilaterian animals (worms, humans, snails, fish, etc.). Furthermore, they possess a third tissue layer between the endoderm and ectoderm, another characteristic reminiscent of
572-416: A single gene . In Tetrahymena , the micronucleus has 10 chromosomes (five per haploid genome), while the macronucleus has over 20,000 chromosomes. In addition, the micronuclear genes are interrupted by numerous "internal eliminated sequences" (IESs). During development of the macronucleus, IESs are deleted and the remaining gene segments, macronuclear destined sequences (MDSs), are spliced together to give
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#1732800762136624-606: A taxon now split because each has a distinctive organization or ultrastructural identity . The Acavomonidia are closer to the dinoflagellate/perkinsid group than the Colponemidia are. As such, the informal term "colponemids", as it stands currently, covers two non-sister groups within Alveolata: the Acavomonidia and the Colponemidia. The Apicomplexa and dinoflagellates may be more closely related to each other than to
676-403: Is actually a structure made up of two components: piles of fibres, and microtubules . This structure is found in different unicellular eukaryotes like paramecium organelles. Digested nutrients from the vacuole pass into the cytoplasm , making the vacuole shrink and moves to the anal pore, where it ruptures to release the waste content to the environment outside of the cell. The cytoproct
728-631: Is found as the sister group to Ventrata / CONthreeP . The class Cariacotrichea was excluded from the analysis, but it was originally established as part of Intramacronucleata . The odontostomatids were identified in 2018 as its own class Odontostomatea , related to Armophorea . Mesodiniea Karyorelictea Heterotrichea Odontostomatea Armophorea Litostomatea Spirotrichea Cariacotrichea Protocruziea Discotrichida Colpodea Nassophorea Phyllopharyngea Oligohymenophorea Prostomatea Plagiopylea Several different classification schemes have been proposed for
780-450: Is guided by long RNAs derived from the parental macronucleus. More than 95% of micronuclear DNA is eliminated during spirotrich macronuclear development. ln clonal populations of Paramecium , aging occurs over successive generations leading to a gradual loss of vitality, unless the cell line is revitalized by conjugation or autogamy . In Paramecium tetraurelia , the clonally aging line loses vitality and expires after about 200 fissions, if
832-470: Is known to cause disease in humans. Ciliates reproduce asexually , by various kinds of fission . During fission, the micronucleus undergoes mitosis and the macronucleus elongates and undergoes amitosis (except among the Karyorelictean ciliates, whose macronuclei do not divide). The cell then divides in two, and each new cell obtains a copy of the micronucleus and the macronucleus. Typically,
884-600: Is moved by the cilia through the mouth pore into the gullet, which forms food vacuoles. Many species are also mixotrophic , combining phagotrophy and phototrophy through kleptoplasty or symbiosis with photosynthetic microbes. The ciliate Halteria has been observed to feed on chloroviruses . Feeding techniques vary considerably, however. Some ciliates are mouthless and feed by absorption ( osmotrophy ), while others are predatory and feed on other protozoa and in particular on other ciliates. Some ciliates parasitize animals , although only one species, Balantidium coli ,
936-445: Is not a permanently visible structure; it appears at the time of defecation and then disappears afterward. In paramecium , the anal pore is a region of pellicle that is not covered by ridges and cilia , and the area has thin pellicles that allow the vacuoles to be merged into the cell surface to be emptied. In ciliates , the anal cytostomes and cytopyge pore regions are not covered by either ridges or cilia or hard coatings like
988-424: Is one of the main components of the cell cortex . Others are the alveoli , small vesicles under the cell membrane that are packed against it to form a pellicle maintaining the cell's shape, which varies from flexible and contractile to rigid. Numerous mitochondria and extrusomes are also generally present. The presence of alveoli, the structure of the cilia, the form of mitosis and various other details indicate
1040-478: Is referred to as "isogamontic" conjugation. In some groups, partners are different in size and shape. This is referred to as "anisogamontic" conjugation. In sessile peritrichs , for instance, one sexual partner (the microconjugant) is small and mobile, while the other (macroconjugant) is large and sessile . In Paramecium caudatum , the stages of conjugation are as follows (see diagram at right): Ciliates contain two types of nuclei: somatic " macronucleus " and
1092-399: Is used for the excretion of indigestible debris contained in the food vacuoles. Most microorganisms possess an anal pore for excretion, usually in the form of an opening on the pellicle to eject out indigestible debris. The opening and closing of the cytoproct resemble a reversible ring of tissue fusion occurring between the inner and outer layers located at the aboral end. An anal pore
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#17328007621361144-522: Is water—in lakes, ponds, oceans, rivers, and soils, including anoxic and oxygen-depleted habitats. About 4,500 unique free-living species have been described, and the potential number of extant species is estimated at 27,000–40,000. Included in this number are many ectosymbiotic and endosymbiotic species, as well as some obligate and opportunistic parasites . Ciliate species range in size from as little as 10 μm in some colpodeans to as much as 4 mm in length in some geleiids , and include some of
1196-470: The Bilateria . Ctenophores possess a functional through-gut from which digested waste products and material distributed via the endodermal canals are expelled to the exterior environment through terminal anal pores, which are specialized to control outflow from the branched endodermal canal system. Ctenophores have no true anus; the central canal opens toward the aboral end by two small pores, through which
1248-786: The Cercozoa . The ellobiopsids are of uncertain relation within the alveolates. Silberman et al 2004 establish that the Thalassomyces genus of ellobiopsids are alveolates using phylogenetic analysis, however as of 2016 no more certainty exists on their place. In 2017, Thomas Cavalier-Smith described the phylogeny of the Alveolata as follows: Heterotrichea Karyorelictea Desmata Spirotrichia Colponemea Acavomonadea Apicomonada Sporozoa Dinoflagellata Perkinsea Alveolata Cavalier-Smith 1991 [Alveolatobiontes] The development of plastids among
1300-403: The anus and mouth of multicellular organisms. The cytopyge's thin membrane allows vacuoles to be merged into the cell wall and emptied. The anal pore is an exterior opening of microscopic organisms through which undigested food waste, water, or gas are expelled from the body. The anal pore is located on the ventral surface, usually in the posterior half of the cell. The anal pore itself
1352-580: The ellobiopsids . In 2001, direct amplification of the rRNA gene in marine picoplankton samples revealed the presence of two novel alveolate lineages, called group I and II. Group I has no cultivated relatives, while group II is related to the dinoflagellate parasite Amoebophrya , which was classified until now in the Syndiniales dinoflagellate order. Some studies suggested the haplosporids , mostly parasites of marine invertebrates, might belong here, but they lack alveoli and are now placed among
1404-617: The germline " micronucleus ". Only the DNA in the micronucleus is passed on during sexual reproduction (conjugation). On the other hand, only the DNA in the macronucleus is actively expressed and results in the phenotype of the organism. Macronuclear DNA is derived from micronuclear DNA by amazingly extensive DNA rearrangement and amplification. The macronucleus begins as a copy of the micronucleus. The micronuclear chromosomes are fragmented into many smaller pieces and amplified to give many copies. The resulting macronuclear chromosomes often contain only
1456-441: The phenotype of the organism). The latter is generated from the micronucleus by amplification of the genome and heavy editing. The micronucleus passes its genetic material to offspring, but does not express its genes. The macronucleus provides the small nuclear RNA for vegetative growth. Division of the macronucleus occurs in most ciliate species, apart from those in class Karyorelictea, whose macronuclei are replaced every time
1508-610: The stramenopiles and Rhizaria among the protists with tubulocristate mitochondria into the SAR supergroup . The most notable shared characteristic is the presence of cortical (near the surface) alveoli (sacs) . These are flattened vesicles (sacs) arranged as a layer just under the membrane and supporting it, typically contributing to a flexible pellicle (thin skin). In armored dinoflagellates they may contain stiff plates. Alveolates have mitochondria with tubular cristae ( invaginations ), and cells often have pore-like intrusions through
1560-594: The 1980s, and this was confirmed in the early 1990s by comparisons of ribosomal RNA sequences, most notably by Gajadhar et al . Cavalier-Smith introduced the formal name Alveolata in 1991, although at the time he considered the grouping to be a paraphyletic assemblage. Many biologists prefer the use of the colloquial name 'alveolate'. Alveolata include around nine major and minor groups. They are diverse in form, and are known to be related by various ultrastructural and genetic similarities: The Acavomonidia and Colponemidia were previously grouped together as colponemids,
1612-493: The Chromerida and the heterokont algae acquired their plastids from a red alga with evidence of a common origin of this organelle in all these four clades. A Bayesian estimate places the evolution of the alveolate group at ~ 850 million years ago . The Alveolata consist of Myzozoa , Ciliates , and Colponemids. In other words, the term Myzozoa, meaning "to siphon the contents from prey", may be applied informally to
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1664-471: The alveolates is intriguing. Cavalier-Smith proposed the alveolates developed from a chloroplast-containing ancestor, which also gave rise to the Chromista (the chromalveolate hypothesis). Other researchers have speculated that the alveolates originally lacked plastids and possibly the dinoflagellates and Apicomplexa acquired them separately. However, it now appears that the alveolates, the dinoflagellates,
1716-484: The balance can swing one way or other at the point of origin of a new phylum from mixotrophic ancestors, causing one ability to be lost. Few algae have been studied for epigenetics . Those for which epigenetic data are available include some algal alveolates. Anal pore In ciliates, the anal pore ( cytopyge ) and cytostome are the only regions of the pellicle that are not covered by ridges, cilia or rigid covering. They serve as analogues of, respectively,
1768-437: The basis that apicomplexans possess a plastid surrounded by four membranes, and that peridinin dinoflagellates possess a plastid surrounded by three membranes, Petersen et al. have been unable to rule out that the shared stramenopile-alveolate plastid could have been recycled multiple times in the alveolate phylum, the source being stramenopile-alveolate donors, through the mechanism of ingestion and endosymbiosis . Ciliates are
1820-603: The cause of aging in P. tetraurelia . Until recently, the oldest ciliate fossils known were tintinnids from the Ordovician period . In 2007, Li et al. published a description of fossil ciliates from the Doushantuo Formation , about 580 million years ago, in the Ediacaran period . These included two types of tintinnids and a possible ancestral suctorian. A fossil Vorticella has been discovered inside
1872-542: The cell divides. Macronuclear division is accomplished by amitosis , and the segregation of the chromosomes occurs by a process whose mechanism is unknown. After a certain number of generations (200–350, in Paramecium aurelia , and as many as 1,500 in Tetrahymena ) the cell shows signs of aging, and the macronuclei must be regenerated from the micronuclei. Usually, this occurs following conjugation , after which
1924-423: The cell is divided transversally, with the anterior half of the ciliate (the proter ) forming one new organism, and the posterior half (the opisthe ) forming another. However, other types of fission occur in some ciliate groups. These include budding (the emergence of small ciliated offspring, or "swarmers", from the body of a mature parent); strobilation (multiple divisions along the cell body, producing
1976-466: The cell line is not rejuvenated by conjugation or self-fertilization. The basis for clonal aging was clarified by the transplantation experiments of Aufderheide in 1986 who demonstrated that the macronucleus, rather than the cytoplasm, is responsible for clonal aging. Additional experiments by Smith-Sonneborn, Holmes and Holmes, and Gilley and Blackburn demonstrated that, during clonal aging, DNA damage increases dramatically. Thus, DNA damage appears to be
2028-696: The cell surface. The group contains free-living and parasitic organisms, predatory flagellates , and photosynthetic organisms. Almost all sequenced mitochondrial genomes of ciliates and apicomplexa are linear. The mitochondria almost all carry mtDNA of their own but with greatly reduced genome sizes. Exceptions are Cryptosporidium which are left with only a mitosome , the circular mitochondrial genomes of Acavomonas and Babesia microti , and Toxoplasma ' s highly fragmented mitochondrial genome, consisting of 21 sequence blocks which recombine to produce longer segments. The relationship of apicomplexa, dinoflagellates and ciliates had been suggested during
2080-456: The ciliate phylum known to be pathogenic to humans is Balantidium coli , which causes the disease balantidiasis . It is not pathogenic to the domestic pig, the primary reservoir of this pathogen. Alveolate The alveolates (meaning "pitted like a honeycomb") are a group of protists , considered a major clade and superphylum within Eukarya . They are currently grouped with
2132-630: The ciliates. Both have plastids , and most share a bundle or cone of microtubules at the top of the cell. In apicomplexans this forms part of a complex used to enter host cells, while in some colorless dinoflagellates it forms a peduncle used to ingest prey. Various other genera are closely related to these two groups, mostly flagellates with a similar apical structure. These include free-living members in Oxyrrhis and Colponema , and parasites in Perkinsus , Parvilucifera , Rastrimonas and
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2184-429: The ciliates. The following scheme is based on a molecular phylogenetic analysis of up to four genes from 152 species representing 110 families: Some old classifications included Opalinidae in the ciliates. The fundamental difference between multiciliate flagellates (e.g., hemimastigids , Stephanopogon , Multicilia , opalines ) and ciliates is the presence of macronuclei in ciliates alone. The only member of
2236-431: The common ancestor of the subset of alveolates that are neither ciliates nor colponemids. Predation upon algae is an important driver in alveolate evolution, as it can provide sources for endosymbiosis of novel plastids. The term Myzozoa is therefore a handy concept for tracking the history of the alveolate phylum. The ancestors of the alveolate group may have been photosynthetic. The ancestral alveolate probably possessed
2288-551: The macronuclei disappear, and haploid micronuclei are exchanged over the bridge. In some ciliates (peritrichs, chonotrichs and some suctorians ), conjugating cells become permanently fused, and one conjugant is absorbed by the other. In most ciliate groups, however, the cells separate after conjugation, and both form new macronuclei from their micronuclei. Conjugation and autogamy are always followed by fission. In many ciliates, such as Paramecium , conjugating partners (gamonts) are similar or indistinguishable in size and shape. This
2340-414: The most morphologically complex protozoans. In most systems of taxonomy , " Ciliophora " is ranked as a phylum under any of several kingdoms , including Chromista , Protista or Protozoa . In some older systems of classification, such as the influential taxonomic works of Alfred Kahl , ciliated protozoa are placed within the class " Ciliata " (a term which can also refer to a genus of fish ). In
2392-585: The operational gene. Tetrahymena has about 6,000 IESs and about 15% of micronuclear DNA is eliminated during this process. The process is guided by small RNAs and epigenetic chromatin marks. In spirotrich ciliates (such as Oxytricha ), the process is even more complex due to "gene scrambling": the MDSs in the micronucleus are often in different order and orientation from that in the macronuclear gene, and so in addition to deletion, DNA inversion and translocation are required for "unscrambling". This process
2444-554: The organism. Directly after secretion of the waste products, deep invagination (deep, canyon-like structure that was the vacuole) is still present. About 10 to 30 seconds after secretion, the vacuole detaches, and a new thin plasma membrane is formed. After a minute has gone by the organisms cytoproct is closed up again and the process is ready to be repeated. Ctnephores are marine animals which superficially resemble jellyfish, but have biradial symmetry and use eight bands of transverse ciliated plates to swim. All ctenophores possess
2496-408: The other parts of the organism. As a food vacuole approaches the cytoproct region it actually starts to flatten out the surrounding cells, and a thin-membrane vacuole allows it to be combined in the cell wall. Once the vacuole attaches to the plasma membrane of the cell wall, the vacuole is emptied. The waste excreted by the cell can come as a membrane-bound packaged ball, or as a stream of debris behind
2548-646: The taxonomic scheme endorsed by the International Society of Protistologists , which eliminates formal rank designations such as "phylum" and "class", "Ciliophora" is an unranked taxon within Alveolata . Unlike most other eukaryotes , ciliates have two different sorts of nuclei : a tiny, diploid micronucleus (the "generative nucleus", which carries the germline of the cell), and a large, ampliploid macronucleus (the "vegetative nucleus", which takes care of general cell regulation, expressing
2600-555: The time it reaches the cytoproct ( anal pore ) is discharged by exocytosis . 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. In some genera, such as Paramecium , these have a distinctive star shape, with each point being a collecting tube. Mostly, body cilia are arranged in mono- and dikinetids , which respectively include one and two kinetosomes (basal bodies), each of which may support
2652-459: Was also photosynthetic. In one school of thought the common ancestor of the dinoflagellates , apicomplexans , Colpodella , Chromerida , and Voromonas was a myzocytotic predator with two heterodynamic flagella , micropores , trichocysts , rhoptries , micronemes , a polar ring and a coiled open sided conoid . While the common ancestor of alveolates may also have possessed some of these characteristics, it has been argued that Myzocytosis
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#17328007621362704-412: Was not one of these characteristics, as ciliates ingest prey by a different mechanism. An ongoing debate concerns the number of membranes surrounding the plastid across apicomplexans and certain dinoflagellates, and the origin of these membranes. This ultrastructural character can be used to group organisms and if the character is in common, it can imply that phyla had a common photosynthetic ancestor. On
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