Peranema
Encyclopedia
Peranema is a genus of free-living flagellate
protist
s, with about 20 species, varying in size between 8 and 200 micrometers. They are found in freshwater lakes, ponds and ditches, and are often abundant at the bottom (benthos
) of stagnant pools rich in decaying organic material. Although they belong to the class Euglenoidea, and are morphologically similar to the green Euglena
, Peranema have no chloroplasts, and cannot feed by 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 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 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 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 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.
with finely-ridged microtubule
s (a structure often referred to as "pellicle strips") arranged in a helical fashion around the body. On 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 swimming, Peranema can creep along by metaboly, progressing with wavelike contractions of 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) to which the flagella are attached. One flagellum is relatively long and conspicuous, and when the Peranema is swimming it is held stiffly in front. At the tip of the flagellum, a short segment beats and flails in a rhythmic manner, causing the Peranema to move forward through the water with a calm, gliding motion. Peranama usually swims 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 the posterior. It does not float 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 Peranemas highly developed feeding apparatus, a cytostomal
sac supported on one side by a pair of rigid rods, fused together at the forward 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 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 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 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 is left of the prey but the tattered remnants of its pellicle.
. In 1881 Georg Klebs
drew a taxonomical distinction between colorless uniflagellates that live by phagotrophy (Peranema and Astasia) and 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 the other two species.
Flagellate
Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...
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, with about 20 species, varying in size between 8 and 200 micrometers. They are found in freshwater lakes, ponds and ditches, and are often abundant at the bottom (benthos
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
) of stagnant pools rich in decaying organic material. Although they belong to the class Euglenoidea, and are morphologically similar to the green Euglena
Euglena
Euglena is a genus of unicellular flagellate protists. It is the best known and most widely studied member of the phylum Euglenozoa , a diverse group containing some 44 genera and at least 800 species. Species of Euglena are found in fresh and salt waters...
, Peranema have no chloroplasts, and cannot feed by autotrophy
Autotrophy
Autotrophy is the ability to be self-sustained by producing food from inorganic compounds. Some bacteria and some archaea have this ability. Inorganic compounds are oxidized directly without sunlight to yield energy. This metabolic mode also requires energy for CO2 reduction, like photosynthesis,...
. 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
Eyespot apparatus
The eyespot apparatus is a photoreceptive organelle found in the flagellate cells of green algae and other unicellular photosynthetic organisms such as euglenids. It allows the cells to sense light direction and intensity and respond to it by swimming either towards the light or away from the...
(stigma), and the paraflagellar body
Eyespot apparatus
The eyespot apparatus is a photoreceptive organelle found in the flagellate cells of green algae and other unicellular photosynthetic organisms such as euglenids. It allows the cells to sense light direction and intensity and respond to it by swimming either towards the light or away from the...
(photoreceptor) that is normally coupled with that organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
. However, while Peranema lack a localized photoreceptor, they do possess the light-sensitive protein rhodopsin
Rhodopsin
Rhodopsin, also known as visual purple, is a biological pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light,...
, 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 the "long-necked" infusoria, along with Lacrymaria olor
Lacrymaria olor
Lacrymaria olor is a protozoan, typically long, that is found in freshwater ponds. Its name means "swan tear" in Latin, and refers to its general shape: namely, a teardrop-shaped body with a small "head" at the end of a long slender "neck"...
and Dileptus
Dileptus
Dileptus is a genus of unicellular ciliate protists, belonging to the class Litostomatea. Members of the genus are found in fresh and salt water...
. 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
Félix Dujardin
-External sources:* @ Encyclopædia Britannica Online...
, who created the genus in 1842, giving it 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 the protist Peranema as Pseudoperanema; whereas protozoologists, following the International Code of Zoological Nomenclature
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
, have continued to call the genus by the name Dujardin gave it.
Appearance and characteristics
Peranemas basic anatomy is that of a typical Euglenid. The cell is spindle or cigar-shaped, somewhat pointed at the anterior end. It has a pelliclePellicle (biology)
The pellicle is a thin layer supporting the cell membrane in various protozoa, protecting them and allowing them to retain their shape, especially during locomotion, allowing the organism to be more hydrodynamic. They vary from flexible and elastic to rigid. Although stiff, the pellicle is...
with finely-ridged 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 (a structure often referred to as "pellicle strips") arranged in a helical fashion around the body. On 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 swimming, Peranema can creep along by metaboly, progressing with wavelike contractions of the body, reminiscent of peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
.
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) to which the flagella are attached. One flagellum is relatively long and conspicuous, and when the Peranema is swimming it is held stiffly in front. At the tip of the flagellum, a short segment beats and flails in a rhythmic manner, causing the Peranema to move forward through the water with a calm, gliding motion. Peranama usually swims 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 the posterior. It does not float 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 Peranemas highly developed feeding apparatus, a cytostomal
Cytostome
A cytostome 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 ciliates and excavates, have cytostomes. Such...
sac supported on one side by a pair of rigid rods, fused together at the forward 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 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 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
Cytostome
A cytostome 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 ciliates and excavates, have cytostomes. Such...
.
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 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
Protoplasm
Protoplasm is the living contents of a cell that is surrounded by a plasma membrane. It is a general term of the Cytoplasm . Protoplasm is composed of a mixture of small molecules such as ions, amino acids, monosaccharides and water, and macromolecules such as nucleic acids, proteins, lipids and...
, 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 is left of the prey but the tattered remnants of its pellicle.
Phylogeny and classification
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 EuglenaEuglena
Euglena is a genus of unicellular flagellate protists. It is the best known and most widely studied member of the phylum Euglenozoa , a diverse group containing some 44 genera and at least 800 species. Species of Euglena are found in fresh and salt waters...
. In 1881 Georg Klebs
Georg Klebs
Georg Albrecht Klebs was a German botanist from Neidenburg , Prussia. His brother was the historian Elimar Klebs.-Life:...
drew a taxonomical distinction between colorless uniflagellates that live by phagotrophy (Peranema and Astasia) and 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
Basal
Basal or basilar is a term meaning base, bottom, or minimum.-Science:* Basal , an anatomical term of location for features associated with the base of an organism or structure...
to the other two species.
Species
- Peranema asperum Playfair
- Peranema asperum var. rectangulare Playfair
- Peranema cryptocercum (Skuja) Popova
- Peranema cuneatum Playfair
- Peranema curvicauda Skuja
- Peranema deflexum Skuja
- Peranema dolichonema
- Peranema glabrum Van Ove
- Peranema granuliferum Penard
- Peranema hyalinum Christen
- Peranema inflexum Skuja
- Peranema kupfferi Skuja
- Peranema limax Christen
- Peranema ovale Lackey
- Peranema pleururum Skuja
- Peranema sacculus Christen
- Peranema trichophorum (Ehrenberg) Stein
- Peranema trichophorum (Ehrenberg) Playfair
- Peranema truncatum Svortzov