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38-405: See text Peranema is a genus of free-living phagotrophic euglenids (Euglenida; Euglenozoa; Excavata ). There are more than 20 nominal species, varying in size between 8 and 200 micrometers. Peranema cells are gliding flagellates found in freshwater lakes, ponds and ditches, and are often abundant at the bottom of stagnant pools rich in decaying organic material. Although they belong to
76-484: A monophyletic group. Phylogenetic analyses often do not place malawimonads on the same branch as the other Excavata. Excavates were thought to include multiple groups: Euglenozoa and Heterolobosea (Percolozoa) or Eozoa (as named by Cavalier-Smith ) appear to be particularly close relatives, and are united by the presence of discoid cristae within the mitochondria (Superphylum Discicristata ). A close relationship has been shown between Discicristata and Jakobida ,
114-438: A central nucleus. The length of the cytopharynx varies during the cell cycle , however the average length is 8 μm. Much like the cytostome, a set of microtubules form an association with the cytopharynx. Two sets of microtubules follow the path of the cytopharynx in cells. These sets of microtubules form a gutter like structure that surrounds the cytopharynx. One side of the cytopharynx is not associated with these microtubules and
152-650: A conspicuous ventral feeding groove with a characteristic ultrastructure , supported by microtubules —the "excavated" appearance of this groove giving the organisms their name. However, various groups that lack these traits are considered to be derived excavates based on genetic evidence (primarily phylogenetic trees of molecular sequences). The Acrasidae slime molds are the only excavates to exhibit limited multicellularity. Like other cellular slime molds , they live most of their life as single cells, but will sometimes assemble into larger clusters. Excavate relationships were always uncertain, suggesting that they are not
190-462: A helical fashion around the body. With this type of pellicle, which is shared by many euglenids, the spiraling microtubular strips are able to slide past one another, giving the organism an extremely plastic and changeable body shape. This permits a type of squirming motility, sometimes referred to as "euglenoid movement" or "metaboly". When it is not gliding or swimming (poorly), Peranema can move by metaboly, progressing with wavelike contractions of
228-485: A more elaborate style of attack. Sometimes, it will press its cytostome against its prey, and then move the rod-organ up and down, using a rasping motion to chew a hole in its victim's cell membrane. After consuming some of the protoplasm , the Peranema may then insert its large flagellum into the hole, using it to churn up the contents of the cell so that they may be more easily sucked out. This continues until nothing
266-485: A narrow longitudinal groove down one side of the cell. The ancyromonad groove is not used for "suspension feeding", unlike in "typical excavates" (e.g. malawimonads, jakobids, Trimastix , Carpediemonas , Kiperferlia , etc). Ancyromonads instead capture prokaryotes attached to surfaces. The phylogenetic placement of ancyromonads is poorly understood (in 2020), however some phylogenetic analyses place them as close relatives of malawimonads. The conventional explanation for
304-773: A phylogenetic tree with the metamonad Parabasalia as basal Eukaryotes. Discoba and the rest of the Eukaryota appear to have emerged as sister taxon to the Preaxostyla, incorporating a single alphaproteobacterium as mitochondria by endosymbiosis. Thus the Fornicata are more closely related to e.g. animals than to Parabasalia. The rest of the Eukaryotes emerged within the Excavata as sister of the Discoba; as they are within
342-407: Is Balantidium coli , a ciliate. In other protozoa, and in cells from multicellular organisms, phagocytosis takes place at any point on the cell or feeding takes place by absorption. The cytostome forms an invagination on the cell surface and is typically directed towards the nucleus of the cell. The cytostome is often labeled as the entire invagination, but in fact the cytostome only constitutes
380-481: Is approximately level with the opening of the flagellar pocket. Ciliophora is a phylum of protozoa. The cytostome in this phyla can be either apical or lateral. The cytostome-cytopharynx complex functions as follows: macromolecules to be taken up by a cell enter the cytostome. Macromolecules then pass into the lumen of the cytopharynx and are transported to the posterior end of the cell where they are put into budding vesicles that are transported to others parts of
418-411: Is deemed the "nude". However, vesicles associate with this side of the cytopharynx. The location of the cytostome in most flagellated protozoa is strongly conserved. The cytostome is located on the anterior end of the cell close to a structure known as the flagellar pocket. The flagellar pocket is also an invagination in the cell and also serves as a site of endocytosis. The opening of the cytostome
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#1732793246019456-401: Is left of the prey but the tattered remnants of its pellicle. When Dujardin created the genus Peranema in 1841, he was unable to detect the second flagellum and classified it with other ostensibly uniflagellate "Eugléniens," Astasia and Euglena . In 1881 Georg Klebs drew a taxonomical distinction between colorless uniflagellates that live by phagotrophy ( Peranema and Astasia ) and
494-457: Is normally coupled with that organelle . However, while Peranema lack a localized photoreceptor, they do possess the light-sensitive protein rhodopsin , and respond to changes in light with a characteristic "curling behaviour." The earliest record of a Peranema is in O.F. Müller 's Animalcula Infusoria of 1786, which describes an "elongated linear" creature, "stretched out at the front." Müller named it Vibrio strictus , placing it among
532-422: Is positioned directly beneath the flagella r pocket membrane and forms a quartet. Equally as important in the function of endocytosis is the structure known as the cytopharynx. The cytopharynx is a long, tube-like structure that forms the invagination associated with the cytostome. While the shape of the cytopharynx is not constant, it is typically directed towards the posterior of the cell, often hooking around
570-437: Is the only known example of an endocytotic organelle being associated with an organelle that is used for locomotion. As mentioned above, the flagellar pocket is another site of endocytosis in flagellated protozoa. The flagellar pocket is an invagination that is formed around the extracellular flagellum. The flagellar pocket is a site of both endocytosis and exocytosis in cells. Many methods have been used in order to visualize
608-416: The "long-necked" infusoria, along with Lacrymaria olor and Dileptus . The species Peranema trichophorum was seen and described in 1838 by C.G. Ehrenberg , who, like Müller before him, took the flagellum for a necklike extension of the body, and placed it in the ciliate genus Trachelius . Peranema was correctly identified as a flagellate by Félix Dujardin , who created the genus in 1842, giving it
646-406: The body, reminiscent of peristalsis . At the anterior of the cell, there is a narrow aperture, opening into a flask-shaped "reservoir", from which the organism's two flagella emerge. At the bottom of this reservoir lie the basal bodies (centrioles) from which the flagella extend. One flagellum is relatively long and conspicuous, and when the Peranema is gliding it is held stiffly in front. At
684-502: The cell. The cytopharynx in this way acts much like a straw that sucks macromolecules to the posterior end of the cell. The passage of macromolecules from the entrance of the cytostome to the posterior end of the cytopharynx takes at least 2 minutes. The cytostome is the main site of endocytosis in Trypanosoma cruzi epimastigotes . The cytostome has also been found to associate with the flagellum of Trypanosoma cruzi . So far, this
722-629: The cells are arranged (they have a distinctive ultrastructural identity ). They are considered to be a basal flagellate lineage. On the basis of phylogenomic analyses, the group was shown to contain three widely separated eukaryote groups, the discobids, metamonads, and malawimonads. A current view of the composition of the excavates is given below, indicating that the group is paraphyletic. Except for some Euglenozoa , all are non- photosynthetic . Most excavates are unicellular, heterotrophic flagellates. Only some Euglenozoa are photosynthetic. In some (particularly anaerobic intestinal parasites),
760-429: The class Euglenoidea , and are morphologically similar to the green Euglena , Peranema have no chloroplasts , and do not conduct autotrophy . Instead, they capture live prey, such as yeast, bacteria and other flagellates, consuming them with the help of a rigid feeding apparatus called a "rod-organ." Unlike the green euglenids, they lack both an eyespot (stigma), and the paraflagellar body (photoreceptor) that
798-439: The cytostome works independently in order to import macromolecules. In these instances, the cytostome imports macromolecules by directly forming vesicles that are imported into the interior of the cell. The cytostome is associated with microtubules that function in maintaining its form. One set of microtubules is arranged in a triplet formation and is located directly beneath the cytostome membrane . A second set of microtubules
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#1732793246019836-511: The cytostome. Eger et al. used gold labeled transferrin molecules in combination with confocal microscopy in order to visualize the cytostome. This experiment showed that labeling with the gold particles was evident at two locations in the cells; one of the locations was the bottom of the cytopharynx, and the other location was in reservosomes in the cell. Another team used ion beam scanning electron microscopy , also known as FIB-SEM followed by three dimensional reconstruction in order to create
874-407: The green uniflagellates that photosynthesize ( Euglena ). This distinction was generally abandoned after the publication, in 1952, of a major revision of the euglenoids. In 1997, a combined morphological and molecular analysis of certain euglenoids identified Peranama trichophorum, Euglena gracilis and Khawkinea quartana as a distinct monophyletic lineage, with P. trichophorum basal to
912-745: The latter having tubular cristae like most other protists, and hence were united under the taxon name Discoba , which was proposed for this supposedly monophyletic group. Metamonads are unusual in not having classical mitochondria—instead they have hydrogenosomes , mitosomes or uncharacterised organelles. The oxymonad Monocercomonoides is reported to have completely lost homologous organelles. There are competing explanations. The malawimonads have been proposed to be members of Excavata owing to their typical excavate morphology, and phylogenetic affinity to other excavate groups in some molecular phylogenies. However, their position among eukaryotes remains elusive. Ancyromonads are small free-living cells with
950-415: The mitochondria have been greatly reduced. Some excavates lack "classical" mitochondria , and are called "amitochondriate", although most retain a mitochondrial organelle in greatly modified form (e.g. a hydrogenosome or mitosome ). Among those with mitochondria, the mitochondrial cristae may be tubular, discoidal , or in some cases, laminar. Most excavates have two, four, or more flagella . Many have
988-636: The name Pyronema , for its pyriform (pear-shaped) body. However, because that name had already been applied to a genus of fungi, he amended the genus to Peranema , formed from the Greek πέρα (a leather purse or sack ) and νήμα (a thread ). Unfortunately, this name had also been claimed earlier, for a genus of ferns first collected in Nepal. As a result, botanists, following the International Code of Botanical Nomenclature , customarily refer to
1026-412: The name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas . Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how
1064-409: The opening of the invagination at the surface of the cell. The rest of the invagination is classified as the cytopharynx. The cytopharynx works in conjunction with the cytostome in order to import macromolecules into the cell. This strong association between the cytostome and cytopharynx is often called the cytostome-cytopharynx complex or the cytopharyngeal apparatus. However, in a small number of cases
1102-439: The origin of the Eukaryotes is that a heimdallarchaeian or another Archaea acquired an alphaproteobacterium as an endosymbiont , and that this became the mitochondrion , the organelle providing oxidative respiration to the eukaryotic cell. Caesar al Jewari and Sandra Baldauf argue instead that the Eukaryotes possibly started with an endosymbiosis event of a Deltaproteobacterium or Gammaproteobacterium , accounting for
1140-509: The other two species. Hassett, Charles (July 1944). "Photo-dynamic Action in the Flagellate Peranema Trichophorum with Special Reference to Motor Response to Light". Chicago Journals . 17 (3): 270–278. JSTOR 30151839 . Excavata Excavata is an extensive and diverse but paraphyletic group of unicellular Eukaryota . The group was first suggested by Simpson and Patterson in 1999 and
1178-575: The otherwise unexplained presence of anaerobic bacterial enzymes in Metamonada. The sister of the Preaxostyla within Metamonada represents the rest of the Eukaryotes which acquired an Alphaproteobacterium. In their scenario, the hydrogenosome and mitosome , both conventionally considered "mitochondrion-derived organelles", would predate the mitochondrion, and instead be derived from the earlier symbiotic bacterium. In 2023, using molecular phylogenetic analysis of 186 taxa, Al Jewari and Baldauf proposed
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1216-583: The posterior. It does not sit freely, like the trailing flagella of Dinema and Entosiphon , but adheres to the outside of the cell membrane, in a groove along its ventral surface. Next to the reservoir, lies Peranema' s highly developed feeding apparatus, a cytostomal sac supported on one side by a pair of rigid rods, fused together at the anterior end. The use of this "rod-organ" in feeding has attracted considerable scholarly interest. Some early researchers speculated that it might assist Peranema in tearing up and consuming its food; while others held that it
1254-441: The protist Peranema as Pseudoperanema ; whereas protozoologists, following the International Code of Zoological Nomenclature , have continued to call the genus by the name Dujardin gave it. Peranema' s basic anatomy is that of a typical euglenid. The cell is spindle or cigar-shaped, somewhat pointed at the anterior end. It has a pellicle with parallel finely-ridged proteinaceous strips underlain by microtubules arranged in
1292-448: The rod-organ had been seen to move back and forth during feeding, Nisbet argued that its primary function is to create suction, drawing prey into the cytostome . In 1997, Richard Triemer returned to the subject, to confirm Chen's opinion that Peranema has a dual feeding technique. It can swallow prey whole, pulling large flagellates through the cytostome, in a manner similar to that proposed by Brenda Nisbet. However, it can also choose
1330-509: The root of a tree is often difficult to pinpoint. Metakaryota Cytostome A cytostome (from cyto- , cell and stome- , mouth) or cell mouth is a part of a cell specialized for phagocytosis , usually in the form of a microtubule -supported funnel or groove. Food is directed into the cytostome, and sealed into vacuoles . Only certain groups of protozoa , such as the Ciliophora and Excavata , have cytostomes. An example
1368-425: The same clade but are not cladistically considered part of the Excavata yet, the Excavata are in this analysis highly paraphyletic. Hodarchaeales Parabasalia Fornicata Preaxostyla Jakobida Heterolobosea Euglenozoa and allies Amorphea (inc. animals, fungi) SAR Archaeplastida (inc. plants) The Anaeramoeba are associated with Parabasalia, but could turn out to be more basal as
1406-416: The tip of the flagellum, a short segment beats and flails in a rhythmic manner, possibly as a mechanism for detecting and contacting potential prey. Peranama usually glides belly-down, without rotating. The second flagellum is difficult to see with bright field microscopy, and was entirely overlooked by early observers. It emerges from the same reservoir as the larger propulsive flagellum, but turns toward
1444-422: Was actually a tubular construction, serving as a cytopharynx . In 1950, Y. T. Chen accurately identified it as a structure separate from the reservoir, which could be used by Peranama to cut and pierce its prey. Brenda Nisbet questioned this, on the grounds that, when examined closely with an electron microscope, the rod-organ is blunt, and therefore an improbable instrument for either cutting or piercing. Since
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