The body has bilateral symmetry. What is radial symmetry? What animals have radial symmetry? Traits of bilaterally symmetrical organisms
What kind of animals are not found on our planet! Some amaze with their size, some surprise with their habits and lifestyle, others are distinguished by their incredible colors.
But the most striking in body structure are still the sea and ocean inhabitants. Their body shape can be very unusual, as it has a special symmetry that is not typical for terrestrial animals. This is radial symmetry.
Types of body symmetry in animals
All animals can be divided into four groups according to the types of body symmetry:
- Animals with bilateral symmetry (bilaterally symmetrical). This group includes most species of terrestrial animals and a significant part of marine ones. The main feature is the arrangement of the body organs symmetrically relative to one plane drawn through it. For example, left and right part body, back and front.
- Radial symmetry of the body (radial symmetry). Characteristic of the ocean depths. The main feature is the structure of the body in such a way that several imaginary lines can be drawn through its central axis, relative to which they will be located symmetrically. For example, the rays of starfish.
- Animals with an asymmetrical body shape. When symmetry is not characteristic at all, the shape constantly changes depending on conditions environment or from the movement of an animal. Typical example -
- Complete lack of symmetry. Such organisms include sponges. They lead an attached lifestyle, can grow across the substrate to different volumes and have absolutely no definite symmetry in their body structure.
Each listed group of organisms derives a certain benefit from its structure. For example, bilateral animals can freely move straight while turning to the sides. Animals with radial symmetry are able to catch prey from different directions. It is convenient for asymmetrical organisms to move around and adapt to environmental conditions.
Radiation symmetry: what is it
Basic distinctive feature Animals that have radial symmetry is due to their unusual body shape. They are usually dome-shaped, cylindrical, or shaped like a star or ball.
Many axes can be drawn through the body of such organisms; relative to each of them there are two completely symmetrical halves. This device allows them to have a number of advantages:
- They move freely in any direction, controlling all directions around them.
- The hunt takes on a larger scale as the prey is felt around the entire body.
- The unusual shape of the body allows it to adapt to the surrounding landscape, blend into it and become invisible.
Radial symmetry of the body is one of the main adaptations for certain classes of animals in the ocean biocenosis.
Characteristics of radial symmetry of the body
The history of the emergence of such a device as radial symmetry of the body goes back to the ancestors of animals. They were the ones who led a completely sedentary, motionless lifestyle and were attached to the substrate. They benefited from such symmetry, and they gave it a start.
The fact that now many actively swimming animals still have radial symmetry indicates that it has not been reduced in the course of evolution. However, its direct purpose this feature no longer fulfills.
The meaning of radial symmetry
Its main purpose in ancestral forms, as well as in modern ones leading an attached lifestyle, is to provide protection from attacks by predators and to obtain food.
After all, animals with radial symmetry were not able to protect themselves, having run away from a predator, they could not hide. Therefore, the only option for protection was to sense the approach of danger from any side of the body and respond in time with protective mechanisms.
In addition, getting food for yourself when you lead a sedentary lifestyle is quite difficult. And radial symmetry allows it to detect the slightest food sources around the entire body and quickly respond to them.
Thus, the radial symmetry of the body provides extremely important mechanisms of self-defense and food for animals that possess it.
Animal examples
There are many examples of animals that have radial symmetry. Their huge species and numerical diversity adorns the sea and ocean bottoms and water columns, allowing people to admire the intricacy of nature and the beauty of the underwater world.
What animals have radial symmetry? For example, such as:
- sea urchins;
- jellyfish;
- holothurians;
- brittle stars;
- dartertails;
- hydra;
- sea stars;
- ctenophores;
- fixed polyps;
- some types of sponges.
These are the most common examples of body radial symmetry in animals. There are other animals, little studied, and perhaps not yet discovered at all, which are characterized by this feature of their physique.
Coelenterates
This type of animal includes three main classes, common feature representatives of which is that they are all animals with radial symmetry. IN life cycles either the stage of a free-swimming jellyfish or the stage of a polyp attached to the substrate predominates. There is one hole, it performs the functions of the oral, anal and genital. Poisonous substances are used for protection
- Hydroid. Main representatives: hydras, hydrants. They lead an attached lifestyle and, like all coelenterates, have two layers in their body structure: ectoderm and endoderm. The middle layer is a gelatinous substance of a watery composition - mesoglea. The body shape is most often goblet-shaped. The main part of life is spent in the polyp stage.
- Jellyfish (scyphoid). The main representatives are all. The body shape is unusual, in the form of a bell or dome. They are also two-layered animals with radial symmetry. The main part of life is spent in the stage of a freely moving jellyfish.
- Corals (polyps). Main representatives: sea anemones, corals. The main feature is the colonial lifestyle. Many corals form entire reefs from their colonies. Single forms also occur, these are different types actinium. The jellyfish stage is not characteristic of these animals at all, only the polyp stage.
In total there are approximately 9,000 species of representatives of this type of animal.
Echinoderms
What other animals have radial symmetry? Of course, everyone knows and very beautiful, unusual and bright echinoderms. This type has about 7 thousand species of these amazing representatives marine fauna. There are five main classes:
- Holothurians resemble worms, but still have radial symmetry. Brightly colored, they move reluctantly along the seabed.
- Brittle stars - resemble starfish, but are more different high mobility and poor color - white, milky and beige colors.
- Sea urchins - may have regular, needle-shaped or may not have spines. The body shape is almost always close to spherical.
- Starfish are five-, eight-, or twelve-rayed animals with pronounced radial symmetry. They are very beautifully colored, lead a sedentary lifestyle, crawl along the bottom.
- Sea lilies are sessile beautiful animals and have the shape of a radial flower. They can separate from the substrate and move to places richer in food.
The lifestyle can be either mobile or attached ( sea lilies). The body is two-layered, the mouth opening serves as the anal and genital openings. The exoskeleton is quite strong, calcareous, and beautifully decorated with colored patterns.
The larvae of these animals have bilateral symmetry of the body, and only adult individuals grow the rays to radiality.
Ctenophores
Most often they are small animals (up to 20 cm), which have an absolutely white, translucent body, decorated with rows of combs. This type of animal is considered one of the most ancient. Ctenophores are predators, eat crustaceans, small fish and even each other. They reproduce very intensively.
In the structure of the body, a third mouth opening appears on the upper part of the body; they lead a free-swimming lifestyle. The most common types are:
- beroe;
- Platyktenidae;
- gastrodes;
- Venus' belt;
- Bolinopsis;
- tjalfiella.
Their radial symmetry, as well as the radial symmetry of some species of coelenterates, is weakly expressed. The body shape resembles a bag or an oval.
Generalization
Thus, radial symmetry of the body is the prerogative of aquatic animals that lead a sedentary or attached lifestyle and gives its owners a number of advantages in hunting prey and evading predators.
" and the subsection " " we published the article "Why are there right-handed people? "Today we will continue the topic and consider an even more global issue - why bilateral symmetry in higher animals and humans? Why aren't we like hydras or starfish? Is it even possible for such a development of evolution when bodies will not have bilateral symmetry? These are the questions we will answer. At the same time, to the question asked in the previous article “Why right hemisphere is responsible for the left side of the body, and the left for the right?”
Why bilateral symmetry? You probably know hundreds of examples of such bodies - horses, dogs, frogs, cats - almost any vertebrate you take will be bilaterally symmetrical. But why? It would be nice to have five-ray symmetry, like a starfish... They say that from one of its severed rays a new individual can grow... Maybe we too would have such an ability?..
Why does bilateral symmetry occur at all?
Answer: This is due to active movement in space. Let us explain in detail:
Some unicellular and multicellular creatures live in the water column. Strictly speaking, for them there are no concepts of “right-left” and “up-down”, because the force of gravity is negligible, and the environment is the same. Therefore, they look like a sphere - needles and outgrowths stick out in all directions to increase buoyancy. Example - radiolaria:
Primitive multicellular organisms attached to the bottom live differently. “Up” and “down” already exist, but the probability of prey or predator appearing is the same on all sides. This is how radial symmetry arises. An anemone, hydra or jellyfish spreads its tentacles in all directions; the concepts of “right” and “left” are nothing for them.
With more active movement, the concepts of “front” and “behind” arise. All the main sense organs go forward, because the likelihood of an attack or prey is greater in front than behind, and everything that has already been indifferently crawled, swam, ran and flew past is not so significant.
An even more active movement implies equal interest in both what is on the left and what is on the right. There is a need for bilateral symmetry. An example that explains the relationship between movement rate and symmetry is sea urchins. Slowly crawling species, like all echinoderms, have radial symmetry.
However, some species have mastered life in sea sand, in which they rummage and move quite quickly. Exactly corresponding to the rule described above, their spherical shell is flattened, slightly elongated and becomes bilaterally symmetrical!
And now the MAIN THING:
In a bilaterally symmetrical animal, both halves should develop equally.
After all any bias in one direction or another is harmful.
It's simple.
If there were no crossing of nerves, and the right hemisphere was responsible for the right side of the body:
The degree of development of each halves depends on the load. Imagine: by chance the right side of the animal’s body moves more, the muscles grow, the blood supply to the right hemisphere is better (after all, there is no crossover of nerves).
How more blood, the more nutrition, and the greater the development of the right half of the brain. Hence, if there were no crossing of nerves, there would be a huge right half of the body and a huge right hemisphere. While the frail left half of the body with grief was controlled in half by the tiny left hemisphere. Well, or vice versa... Agree, the hybrid would be noble - and non-survival.
Therefore, it is more survivable when the right hemisphere controls the left half of the body. Then stimulation of the right hemisphere will improve the left side of the body! Thus, the growth of one of the two symmetrical parts of the body, as it were, “pulls up” the other, thereby ensuring their uniform, coordinated development.
General conclusion:
Active movement gives rise to bilateral symmetry.
Consequently, if we lived in other bodies (hydra, jellyfish, starfish, etc.), and led the same active lifestyle, then we would again have bilateral symmetry.
Just like that, no matter how sad it is :)
1) Coelenterates are three-layered, invertebrate animals.
2) Among them there are both free-floating forms and those attached to the substrate.
3) They reproduce only asexually.
4) Include classes: hydroids, scyphoids, flagellates.
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1. Annelids are the most highly organized animals among other types of worms.
2. Annelids have an open circulatory system.
3. Body annelids consists of identical segments.
4. Annelids have no body cavity.
5. The nervous system of annelids is represented by the peripharyngeal nerve ring and the dorsal nerve cord.
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2. Bovine tapeworms are classified as tapeworms.
3. The body of the bovine tapeworm has a segmented structure.
4. The bovine tapeworm is well developed digestive system and he is actively feeding.
5. The main host of bovine tapeworm is cattle.
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1. Flatworms are three-layered animals.
2. The type of flatworms includes white planaria, human roundworm and liver fluke.
4. Their nervous system is poorly developed.
5. Flatworms are dioecious animals that lay eggs.
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1. The main classes of arthropods are crustaceans, arachnids, and insects.
2. Insects have four pairs of legs, and arachnids have three pairs.
3. Crayfish has simple eyes, while the cross spider has complex eyes.
4. Arachnids have arachnoid glands on their abdomen.
5. The cross spider and the cockchafer breathe using lung sacs and tracheas.
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1. The class of arachnids is the most numerous class of the arthropod phylum.
2. The body of arachnids has a cephalothorax and abdomen.
3. Ticks have a fused body.
4. There are three pairs of walking legs.
5. All spiders lead a terrestrial lifestyle.
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1. The features that distinguish birds from reptiles include the progressive development of the organs of vision, hearing, and coordination of movements.
2. Birds have somewhat worse developed thermoregulation than reptiles.
3. The four-chambered heart of birds has an incomplete septum in the ventricle.
4. Adaptations of birds for flight include: a streamlined body shape, wings filled with dense bone material, the presence of gas exchange in both the lungs and air sacs.
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The housefly is a two-winged insect, its hind wings have turned into halteres. Oral apparatus licking type, the fly feeds on semi-liquid food. The fly lays eggs on rotting organic matter. Her larva white, has no legs, eats food waste, grows quickly and turns into a red-brown pupa. An adult fly emerges from the pupa.
What species criteria are described in the text? Explain your answer.
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3. Flatworms have an elongated, flattened body.
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1. Flatworms are three-layered animals.
2. The phylum Flatworms include white planaria, human roundworm and liver fluke.
3. Flatworms have an elongated, flattened body.
4. Tapeworms have a well-developed digestive system.
5. Flatworms are dioecious animals that lay eggs.
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1. Fish are aquatic chordates.
2. The support of the body of all fish is the internal cartilaginous skeleton
3. Fish breathe through gills.
4. There are two circles of blood circulation in the circulatory system, and only venous blood in the heart.
5. The central nervous system of fish has the form of a tube, the front part of which is turned into forebrain, consisting of 5 departments.
6. Most fish are hermaphrodites.
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1. The mammalian nervous system is characterized by a high degree of complexity. 2. The cerebellar hemispheres are especially developed in the brain, which ensures the complexity of mammalian behavior. 3. Mammals developed an inner ear for the first time, which led to dramatic improvements in animal hearing. 4. All mammals, except the first animals, are viviparous animals. 5. Babies develop in the placenta, which is located in abdominal cavity. 6. Mammals that develop a placenta are called placentals.
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1. Fish are cold-blooded animals that have a streamlined body shape and breathe through gills. 2. Most fish species existing on Earth have a cartilaginous skeleton. 3. The circulatory system of fish is closed, and the heart consists of a ventricle and atrium. 4. All fish have two circles of blood circulation. 5. Venous blood flows into the heart of the fish, which is saturated with oxygen in the gills. 6. The direction of water flow and vibration of water are perceived by fish by their balance organs.
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1) The appearance of the first representatives of the type Flatworms was preceded by the appearance of a number of large aromorphoses. 2) Flatworms have developed a two-layer body structure - the basis for the formation of many organs and organ systems. 3) They developed radial symmetry of the body, ensuring free swimming in water. 4) Orientation in space was facilitated by the emergence of sensory organs and a diffuse nervous system. 5) Digestive and excretory systems appeared. 6) Permanent gonads were formed, which determined the most effective forms of sexual reproduction.
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1. Kangaroo is a representative of marsupial mammals. 2. They live in Australia and South America. 3. Kangaroos feed mainly on insect larvae. 4. After giving birth, the baby kangaroo crawls into the pouch where it feeds.
milk. 5. This method of gestation is due to the fact that kangaroos have a poorly developed placenta. 6. When moving, the kangaroo rests on four legs, which allows it to make long jumps.
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1. The mole lives in underground passages, which it digs itself. 2. Due to his lifestyle, he has a number of adaptations. 3. The mole's paws are adapted for rapid movement. 4. At the same time, the mole’s sense of smell and vision are very weak. 5. This is explained by the fact that the mole does not use them for orientation in space. 6. A mole's whiskers are necessary for its sense of touch.
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1. The phylum Flatworms include white planaria, pork tapeworm, echinococcus and earthworm. 2. Free-living worms differ from parasitic forms in structure, lifestyle and other features. 3. The white planaria is an active predator. 4. She has a through intestine with oral and anal openings. 5. With an active lifestyle, the white planaria needs a lot of energy, so it has a well-developed respiratory system.
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1. The appearance of the first representatives of the type Flatworms was accompanied by a number of large aromorphoses. 2. The most important of them was the emergence of a circulatory system in flatworms. 3. A primary body cavity has appeared. 4. The free movement of these animals in water was ensured by radial symmetry. 5. Progress for flatworms was ensured by the emergence of the stem nervous, digestive and excretory systems of organs. 6. The development of the reproductive system led to a fairly high fertility of animals.
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1. Sharks are a superorder of cartilaginous fish with the following distinctive features: an elongated body more or less torpedo-shaped, a large caudal fin and well-developed gill covers.
2. To date, more than 450 species of sharks are known. 3. The whale shark is the largest known fish (its length reaches 20 meters) and the largest marine predator. 4. Representatives of the superorder are widely distributed in the seas and oceans, from the surface to depths of more than 2000 meters. 5. Sharks mainly live in fresh water. 6. Most sharks are so-called true predators, but 3 species are filter feeders.
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1. Turtles are one of two orders of Pre-smy-ka-yu-shchih-sya, the fossil remains of which can be traced back for more than 220 million years. 2. These animals are distributed in tropical and temperate climate zones almost throughout the Earth. 3. A distinctive feature of turtles is the pan-tsir, which serves as their main protection from enemies. 4. From an ecological point of view, turtle species are divided into sea and land turtles, but land turtles always live in fresh water. 5. All types of turtles are poisonous. 6. Many species of turtles are under threat of extinction to varying degrees and are protected.
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1. Coelenterates are two-layered multicellular animals. 2.They have bilateral symmetry. 3. Coelenterates include freshwater hydra, cornet jellyfish, white planaria, and sea anemone. 4. Coelenterates have a mesh (diffuse) nervous system. 5. Among the coelenterates, there are both free-swimming organisms and attached forms. 6. Stinging cells needed for food capture and movement.
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1. Perch is a primary aquatic animal, a whale is a secondary aquatic animal. 2. Primary aquatic animals have lateral line organs that sense pressure, direction of movement, and speed of water flow. 3. The whale's forelimbs turned into pectoral fins 4. The hind limbs of the whale are modified into a caudal fin. 5. Perch and whale have gill breathing. 6. In whales, the pelvic bones are attached to the sacral spine.
Bilateral symmetry is the identical arrangement of body parts of an organism in the left and right halves on either side of the central axis or plane. Figuratively speaking, if you draw a line from the head to the tail of an organism, both sides are mirror images of each other. In this case, the organism exhibits bilateral symmetry, which is also known as plane symmetry, since one plane divides the organism into mirror-image halves. We'll learn all about bilateral symmetry and look at some examples. We will also discuss the main advantages.
Definition of symmetry
Symmetry refers to the orientation of an organism based on a plane or around an axis. Considering various shapes and the orientation of various organisms, scientists have come up with three main types of symmetry:
- The first type is radial symmetry. With this type, the body plan is based on an axis. In other words, the body is oriented so that it is reflected from behind an imaginary line through the center of the body. These organisms have a top and a bottom, but they do not have a left and right side, a front and a back. A couple of examples of radial symmetry are starfish, jellyfish and sea anemones.
- There are some organisms that exhibit no symmetry at all. They are classified as asymmetrical. The only animals that truly belong to this classification are sponges.
- The last type of symmetry is bilateral symmetry. This is when the body plan can be divided along a plane that divides the animal's body into right and left sides, which are mirror images of each other. Let's look at this type of symmetry a little more closely.
Examples of bilateral symmetry
So now you can think of different animals that exhibit bilateral symmetry. Man is the first example we will discuss. Yes, we humans are an example of bilateral symmetry. This can be seen quite simply. Go and look in the mirror and see for yourself. We could draw a line right down the middle of your body, right through your nose, and split you into right and left mirror images. Even your brain can be divided into equal right and left sides.
Let's look at another example. Do you have a dog or cat? They also have bilateral symmetry. Other examples you might not have thought of are sharks, butterflies and ants.
Benefits of Bilateral Symmetry
So there are actually some real benefits to bilateral symmetry. The fact that we have two eyes and ears means that we can see and hear more than most animals with radial symmetry. Bilateral symmetry also determined the formation of the head and tail region. This means that everything can go in one end and come out the other, unlike those organisms that must use the same hole. Without going into too much detail, let's just say we're all very excited about it.
Another benefit is that bilateral symmetry allows for the development of a more thorough nervous system that can control the body. Many animals have bilateral body symmetry, meaning that they can be divided into matching halves by drawing a line down the center. In this respect, arthropods are built like humans: the right half of an arthropod is a mirror image of the left half. This is bilateral symmetry.
Bilateral and radial symmetry
Most animals on the planet exhibit bilateral symmetry. This is what people have. It is different from radial. Radially symmetrical organisms are like the shape of a pie, where each piece is almost identical, although they do not have a left or right side. Instead, they have a top and bottom surface. Organisms that exhibit radial symmetry are, for example, corals, jellyfish and sea anemones, sea urchins and starfish.
Traits of bilaterally symmetrical organisms
Organisms that have bilateral symmetry exhibit front and back, top and bottom, and left and right sides. They generally move faster than animals that do not exhibit bilateral body symmetry. It also has improved vision and hearing capabilities compared to those with radial symmetry.
Basically all marine organisms, including all vertebrates and some invertebrates, have bilateral symmetry. This includes marine mammals such as dolphins and whales, fish, lobsters and sea turtles. Interestingly, some animals have one type of body symmetry when they are the first life forms, but they develop differently as they grow.
There is one marine animal that exhibits no symmetry at all: sponges. These organisms are multicellular, but remain the only asymmetrical animals. This means there is no place in their bodies where you can split them in half and see mirror images.