The most important feature of sarcopoda is that the cytoplasm of the insect body can extend to form pseudopods, which are the organelles for its movement and feeding.There is a thin cell membrane on the body surface, which makes the insect body very elastic, and can change the shape of the insect body and make deformation movement.Most species live in free living, while minority species live in groups. Freshwater and seawater are distributed, and few species are parasitic.
Sarcopoda has a simple structure and a fewOrganelle, seems to be the most primitiveprotozoan, but many types have complex“bones”Structure, all areHeterotrophic, appearing in life historyFlagellumThe gamete stage of the sarcopoda may beFlagellatesMore evolution.
Chinese name
Sarcopoda
Foreign name
Sarcodina
Features
The cytoplasm of the worm body can extend to form pseudopods
Many animals of the class Sarcopoda have an unstable body shape and a thin layer on the body surfacecell membrane, such as naked amoeba living on the surface of ponds, streams and silt——Amoeba magna(Amoeba proteus), the insect body can constantly change its shape. Any part of the insect body can extend to form pseudopods. The direction of pseudopods stretching out represents the temporary front end of the body. Because new pseudopods can be constantly stretched out, the body shape is not fixed. The pseudopods of the big amoeba are short and thick, with a tight end, which contains flowing cytoplasm. This kind of pseudopods is called leaf shapePseudopodia（lobopodium）。stayoptical microscopeThe insect body can be obviously divided into colorless and transparent ectoplasm (entoplasm) andEndoplasmEndoplasm contains contractile vesicles, food vesicles and particles of different sizes.The nucleus of a large amoeba is disc shaped, usually in the endoplasm in the center of the body.
The structure of many species of Sarcopoda is more complex than that of naked amoeba. The surface of the insect body can form different shapes of shells or inner shells from different substances. Some speciescell surfaceIt can secrete mucus and stick fine sand particles to form a sandy shell, such asSand beetle（Difflugia）；Or the cytoplasm secretes chitin to form a chitin shell, such asArcella (Arcella), etc;Or secrete calcium carbonate from the cytoplasm to form a calcium shell with one or more compartments, such asForaminifera（Foraminiferida）；This calcareous shell is arranged in various forms.Others can form siliceous shells, or siliceous shells, such as Euglypha;Or the siliceous inner shell, located in the cytoplasm, is called the central capsule, such as Heliozoa;Other species can extend long bone needles outward, such asRadiolarians（Radiolaria）。
Third
The morphology of pseudopodia is also different. The leaf shaped pseudopodia of amoeba is formed by both the ectoplasm and the endoplasm.Some shelled amoeba (Testacea) pseudopods are long and thin, with sharp ends, and only composed of ectoplasm. These pseudopods are called filopodium.ForaminiferaThe pseudopodium is also thin and long as silk, but then the pseudopodium branches again, and the branches connect with each other to form a network or root shape. This pseudopodium is called rhizopodium.The pseudopods of heliworms and radiolarians are also thin and long as silk. There is a bunch of microtubules in the pseudopods to form an axis rod for support. The surface of the pseudopods is a thin layerProtoplasmThe pseudopodium can be shortened or withdrawn when necessary, so the shaft is not a bone structure. This pseudopodium is called axopodium.
Sports mode
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The locomotor organelles of Sarcopoda are pseudopods. Due to the different structures of pseudopods, their locomotion modes are also different.The "deformation movement" usually refers to the movement mode of lobopod.This kind of movement is very clear in the amoeba.There is an extremely thin cell membrane on the body surface of the amoeba. The cytoplasm is divided into the ectoplasm and the endoplasm, and the endoplasm can be divided into solid plasmagel and liquid plasmasol.During the movement, the gelatine at the back end of the insect body produces liquid pressure due to the contraction of the protein, forcing the lysosome to flow forward, and at the same time extending the pseudopodium.The top of the pseudopodium forms a hyaline layer.The pressure decreases after flowing to the front end,GelatinousThinned, the lysosome in the transparent layer area flows back from front to back, and the lysosome turns into gelatine again. The gelatine at the back end of the body also partially liquefies to form lysosome, thus forming deformation movement repeatedly.There are still different views on the mechanism of deformation movement.One view is that the power of movement comes from the contraction of the body's back end gel;Another view is that the power is from the contraction of the front-end lysosome to drag the cytoplasm to flow in the direction of pseudopodium, because the gel has less viscosity.Recently usedelectron microscopeObserve the section of amoeba and find that it contains two kinds of microfilaments, thick and thin, with the length of 16nm and 7nm respectively. It is similar to the coarse myosin filament and thin myosin filament of striated muscle of vertebratesActin filamentThe contraction of muscle is powered by ATP and moves by the sliding of actin filament on myosin filament. The movement of amoeba may also move by the sliding of muscle filament in pseudopodium.The silk, root and axial pseudopods are different from leaf pseudopods because they are composed only of ectoplasm, or have a shaft in them.Under the light microscope, with the aid of the flow of particles in the pseudopodium, it can be seen that protoplasm flows in two opposite directions in the pseudopodium, and flows from the base to the end on one side of the pseudopodium;The opposite side flows from the end to the base.
The species of benthic life crawls forward by dragging its body with pseudopods.The vertical movement of the fully floating species in water is regulated by increasing or reducing the bubbling of the outer substance and the change of the oil droplets in the inner substance.Horizontal movement relies on water flow or wind force. Its pseudopods are not mainly for movement, but as feeding organelles. The extension and contraction of axial pseudopods only play an auxiliary role in movement.
Nutrition requirements
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Except for the parasitic species, the other species of Sarcopoda are all animal nutrition.Food includes bacteria, algae, other protozoa, and even small multicellular animals.When feeding, the species with leaf shaped pseudopodia rely on the pseudopodia to form a cup around the food, and the pseudopodia gradually extend close to the food until the food is completely enclosed in the protoplasm to form a food bubble, which contains a certain amount of water to suspend the food in the water;When the species with silk pseudopods feed, the pseudopods cling to the food and are surrounded by food bubbles without water;In root type and axial type pseudopods, when the pseudopods touch food, they are immediately adhered to by the particles on the surface of the pseudopods and quickly surrounded by the mucus membrane on the surface. The mucus membrane contains lysosomes, which can anaesthetize and digest the catch, form food bubbles, and then enter the cytoplasm of the worms. The food bubbles are temporary digestive organelles of Sarcopoda,Endoplasmic acid and various digestive enzymes are injected into it for food decomposition and digestion;For the species with central capsule, the food bubble is digested in the protoplasm outside the capsule. The undigested food residue is left at the back end of the body with the flow of protoplasm, and finally discharged out of the body through the cell membrane. The process of food residue being discharged is called excretion.4、 Reproduction and life history
Asexual reproductionIt is the main reproductive mode of Sarcopoda, mainly divided into two or more divisions.Different species split in different ways.The asexual reproduction of naked amoebas is the mitosis of cells.When the shelled amoeba divides, some cytoplasm flows out of the shell mouth first, and forms a new shell outside the shell. After the initial formation of the new shell, the cytoplasm and nucleus undergo mitosis again to regenerate their lost parts, and finally form two new individuals, one of which has the original shell, and the other has a newly formed shell, such as scale crustacean.The asexual reproduction of radiolaria is similar to that of amoeba crustacea. One new individual receives the original central capsule, and the other new individual forms the central capsule again. The spicule part is either allocated to two daughter cells, or one daughter cell forms the spicule again.Some multinucleate solar worms and multinucleate amoebas divide into many cells. When dividing, there is a part of cytoplasm around each nucleus, and finally the mother cell breaks down to form many new individuals.
The sexual reproduction of Sarcopoda exists in all animals except naked amoeba.For example, in the sexual reproduction of Actinophrys, the axonopod retracts, the body forms a cyst, and cell division is carried out in the cyst to form two daughter cells. Later, the two daughter cells carry out meiotic division (meiosis) respectively, which involves only the nucleus, and the number of chromosomes is reduced from 44 to 22,The contents of a daughter cell nucleus are thrown out as a polar body, and only one nucleus of each daughter cell develops into a gamete nucleus, and then the gamete nuclei of two daughter cells fuse to form a zygote nucleus, and the number of chromosomes returns to 44, finally forming a new individual.
ForaminiferaThe sexual reproduction is quite complicated and consistent.In most foraminifera with multiple shell chambers, there are dimorphism, that is, there are two forms of individuals.One form is the globular type, which has a small proloculum. The globular type contains multinucleated cells. It produces many individuals by asexual reproduction. This individual has a large embryonic chamber, so it is called the large globular type. When the large globular type matures, it can produce many swimming gametes with double flagella. When the gametes of different individuals combine, they form a zygote,The life cycle of foraminifera is completed by the development of zygotes into globular individuals, so the globular type is called asexual generation, and the large globular type is called sexual generation. The asexual generation alternates with the sexual generation, which is called metagenesis. The life cycle and reproductive mode of foraminifera with single shell chamber are the same as those with multiple shell chambers, but there is no difference in the morphology of embryo chamber between the large globular type and the small globular type.
Moisture regulation
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The freshwater species of Sarcopoda all have telescopic bubbles, while the marine and parasitic species generally do not.The number may range from one to many. The drainage of water from contractile vesicles can occur at any part of the body surface. Amoebas have only one or 1-2 contractile vesicles. They can collect excessive water in the body and discharge it out of the body with the flow of protoplasm to maintain the balance of water in the body.
Behavioral action
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Sarcopoda can produce certain behavioral responses to stimuli in the external environment, including contact, heat, light, temperature, chemistry and so on.When any point of the amoeba body touches the stimulation of solid substances, it will immediately change the direction of movement. When encountering solid substances, suspended living species will immediately extend pseudopods until they climb onto solid substances;Appropriate temperature will promote the amoeba to speed up its movement, while too high or too low temperature will inhibit its movement.Appropriate light stimulation causes the gelatinization of the sol in the stimulated part, and increases the elasticity of the local gelation;The stimulation of any trace chemical substance will make them escape. If the amoeba is moved from the culture medium to clean water, it will quickly become radioactive. When an appropriate amount of sodium chloride is added to the clean water, its body shape will return to normal.In short, the response of amoebas to stimuli is called negative taxis when they escape, and the response is called positive taxis when they tend.Sarcopoda has no sensory organelles. The behavioral responses it produces indicate that protoplasm is irritable to environmental stimuli.
Species subheading
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According to the difference of pseudopodia, sarcopoda can be divided into two subclasses.
Rhizopoda(Rhizopoda) pseudopods are leaf shaped, silk shaped and root shaped, but have no axis. They live in fresh water or sea water, and few are parasitic in insects, vertebrates and human digestive tract.
(1) Amoebina
The body is exposed and its shape changes with the flow of protoplasm, and pseudopodia is formed at the same time.Pseudopodial leaf type, with widespread cysts.Most species live in fresh water and a few live in the sea, such as the common big amoeba, acanthamoeba, and Hartmannilla.Few amoebas are parasitic oninvertebrateAnd vertebrates, such as Endamoeba parasitic in termites and cockroachesAmoeba dysenteriae（Entamoeba histolytic） 。There are trophozoite and cyst stages in the life cycle of amoebas in dysentery.Cyst is the stage of transmission, in which there are four nuclei. When a person eats the capsule by mistake, the capsule breaks in the human small intestine, and four nuclei are released, forming small trophozoites, which feed on bacteria in the intestinal cavityAsexual reproductionMore small trophozoites or large trophozoites are formed.The large trophozoite invades the intestinal wall, dissolves intestinal tissue, engulfs tissue and red blood cells, and causes intestinal wall abscess and stool abscesses.So it is also calledAmebic dysentery, or dysentery.The large trophozoite can also invade the liver, lung and other organs, and cause the abscess of the organ. In the intestine, only the small trophozoite can form a cyst, which is excreted with the host feces and spread.
(2) Testacea
A single chambered shell composed of chitin or pseudochitin outside the body, or a sand shell formed by foreign substances such as mucus adhering to sand particles outside the body.One end of the shell is provided with a large hole through which the pseudopods protrude, and the pseudopods are leaf shaped or silk shaped.Asexual reproductionIt is vertical dichotomy or horizontal dichotomy.Sexual reproduction isHeterogamyHowever, the gametes are also amoeba like.Encapsulation is also common, mainly distributed on the surface of fresh water, sea water and wet soil. The common representative species are Arcella vulgaris, whose shell is semicircular and yellowish brown, and the insect body protrudes protoplasmic filaments to fix in the shell.Euglypha strigosa.The shell is composed of siliceous plates with long spines protruding from the shell.Difflugiaoblonga is a kind of shell formed by foreign sand particles being glued by colloid. The structure of the insect in the shell is similar to that of amoeba.
(3) Foraminiferida
Single or multi chambered shells composed of calcium carbonate or pseudochitin have various shapes, including arthropod type, circular type, spherical type, bottle type, spiral type, etc.The multi chambered shell is formed by the continuous secretion of embryo shell cells in a certain direction and arrangement.The chambers in the shell are separated by calcareous plates, but there are holes on the plates to connect the protoplasm in the shell.The cytoplasm in the shell contains one or more nuclei. The outer surface of the shell chamber is covered with an extremely thin layer of ectoplasm. Pseudopods, pseudopods root type, protrude through the shell mouth and the protoplasm outside the shell.Few live in fresh water, such as Allogromia, which has a single shell.Most of them live in the sea, such as Globigerina.It is estimated that there are about 20000 species of foraminifera.Most foraminifera live benthic or floating in the ocean. Their shells and bodies form foraminiferal ooze on the seabed, covering 1/3 of the world's oceans, with a depth of about 4000m.If this limit is exceeded, the calcareous shell will be easily dissolved due to the greater pressure of water and higher concentration of CO2.
Radiopoda(Actinopoda) has axial pseudopodia, lives in fresh water and sea water, and most of them live in floating.
The body is spherical, mainly floating in fresh water, with axial pseudopods, on which there are rows of particles, and pseudopods are mainly used as predatory organelles.The cytoplasm can be clearly divided into a highly vesicular outer layer and a granular dense inner layer.The outer layer contains one to several telescopic bubbles, and the inner layer contains food bubbles, nuclei, symbiotic algae, etc.Some species are surrounded by pseudochitin cysts. Common species are Actinosphaerium, Actinophrys sol, etc.
(2) Radiolaria
The worm body is also spherical, and the largest worm body diameter can reach 5mm.All of them live in the sea, and there is a central capsule composed of chitin or pseudochitin in the body. The central capsule divides the cytoplasm into inner and outer parts. The outer part of the capsule is surrounded by many large sticky bubbles formed by adhesive substances, which are full of mucus.The part outside the capsule has nutritional function, and the part inside the capsule has reproductive function. In fact, there are holes on the central capsule, so that the protoplasm inside and outside can communicate.Pseudopodia is also axial type, and some species also have silk type.Some species also have a grid shaped shell composed of siliceous or strontium sulfate surrounding the body surface.Radial long bone needles protrude from the center of the worm body to the periphery, and form a skeleton together with the outer mesh shell.Single or multi-core, the nucleus is located in the capsule. Radiolarians can also form radiolarian ooze on the seabed, which can be distributed deeper than foraminiferal ooze, because its shell is not calcium carbonate but organic matter, and can withstand greater sea water pressure, representing species such as Acanthomethra elasticum and Hexaconus serratus.
