What kind of animals are not found on our planet! Some are striking in their size, someone is surprised by habits and lifestyle, others are incredible in color.
But the most striking in the structure of the body are still sea and ocean inhabitants. Their body shape can be very unusual, as it has a special symmetry that is not characteristic of terrestrial animals. This is ray symmetry.
Types of body symmetry in animals
All animals by types of body symmetry can be divided into four groups:
- Animals with bilateral symmetry (bilaterally symmetric). This group includes most species of terrestrial animals and a significant part of marine animals. The main feature is the location of the organs of the body symmetrically with respect to one plane drawn through it. For example, the left and right side of the body, the back and front.
- Radial symmetry of the body (ray symmetry). It is characteristic of animals of the sea and ocean depths. The main feature is the body structure in such a way that several imaginary lines can be drawn through its central axis, relative to which parts of the body will be located symmetrically. For example, the rays of starfish.
- Animals with an asymmetric body shape. When symmetry is not characteristic at all, the shape constantly changes depending on environmental conditions or on the movement of the animal. A typical example is the common amoeba.
- Lack of symmetry completely. These organisms include sponges. They lead an attached lifestyle, can grow on a substrate into different volumes and have absolutely no certain symmetry in the structure of the body.
Each listed group of organisms derives a certain benefit for themselves from its structure. So, for example, bilateral animals can freely move directly, turning to the sides. Animals with radial symmetry can catch prey from different angles. It is convenient for asymmetric organisms to move around and adapt to environmental conditions.
Beam symmetry: what is it
The main distinguishing feature of animals with radial symmetry is their unusual body shape. They are usually domed, cylindrical or in the shape of a star or a ball.
Many axes can be drawn through the body of such organisms, with respect to each of them there are two completely symmetrical halves. Such a device gives them the opportunity to have a number of advantages:
- They move freely in any direction, controlling all sides around them.
- Hunting takes on a larger scale, as prey is felt around the whole body.
- The unusual shape of the body allows you to adapt to the surrounding landscape, merge into it and become invisible.
The radiation symmetry of the body is one of the main adaptations for certain classes of animals of the ocean biocenosis.
Characterization of the radial symmetry of the body
The history of the emergence of such an adaptation as the radial symmetry of the body has its roots in the ancestors of animals such as Enteric. It was they who led a completely sedentary, motionless lifestyle and were attached to the substrate. Such symmetry was beneficial for them, and they gave it a start.
The fact that now many actively swimming animals still have radiation symmetry indicates its irreducibility during evolution. However, this feature does not fulfill its intended purpose.
The value of beam symmetry
Its main purpose in ancestral forms, as well as in modern, leading an attached lifestyle, is to provide protection against attacks by predators and to obtain food.
After all, animals with radiation symmetry were not able to protect themselves by running away from a predator, and could not hide. Therefore, the only protection option was to feel the approach of danger from any side of the body and respond in time to protective mechanisms.
In addition, it is quite difficult to get food for yourself when you lead a sedentary lifestyle. And radial symmetry allows you to capture the smallest food sources around the whole body and quickly respond to them.
Thus, the radiation symmetry of the body provides extremely important mechanisms of self-defense and nutrition for animals that possess it.
Examples of animals
There are many examples of animals with radial symmetry. Their huge species and numerical diversity adorns the sea and ocean bottoms and water column, allows a person to admire the intricate nature and the beauty of the underwater world.
Which animals have radiation symmetry? For example, such as:
- sea urchins;
- jellyfish
- holothuria;
- ophiura;
- snaketail;
- hydras;
- sea stars;
- ctenophores;
- motionless polyps;
- some types of sponges.
These are the most common examples of radiation symmetry of the body in animals. There are other animals, poorly understood, and, possibly, not yet discovered at all, which are characterized by such a constitutional feature.
Coelenterates
This type of animal includes three main classes, a common feature of the representatives of which is that they are all animals with radiation symmetry. In the life cycles, either the stage of the free-floating jellyfish or the stage of the polyp attached to the substrate predominates. One hole, performs the function of mouth, anal and genital. For protection use poisonous stinging cells.
- Hydroid. Key representatives: hydras, hydrants. They lead an attached lifestyle, have, like all the intestinal cavities, two layers in the structure of the body: ectoderm and endoderm. The middle layer is a gelatinous substance of a watery composition - mesogley. The shape of the body is most often goblet. The main part of life is in the polyp stage.
- Jellyfish (scyphoid). The main representatives are all types of jellyfish. The shape of the body is unusual, in the form of a bell or dome. They are also two-layer animals with radiation symmetry. The main part of life passes in the stage of a freely moving jellyfish.
- Corals (polyps). The main representatives: sea anemones, corals. The main feature is a colonial lifestyle. Many corals form entire reefs from their settlement colonies. Single forms are also found, these are different types of sea anemones. The jellyfish stage is not at all characteristic of these animals, only the stage of polyps.
In total, there are approximately 9,000 species of representatives of this type of animal.
Echinoderms
What other animals have radiation symmetry? Of course, everyone knows and is very beautiful, unusual and bright echinoderms. This type has about 7 thousand species of these amazing representatives of marine fauna. There are five main classes:
- Holothuria - resemble worms, but nevertheless they have ray symmetry. Brightly colored, moving reluctantly along the seabed.
- Ophiuras resemble starfish, but are distinguished by higher mobility and poverty of color - white, milky and beige colors.
- Sea urchins - may have a regular, needle-shaped outer skeleton, or may not have needles. The shape of the body is almost always close to spherical.
- Starfish are five, eight, or twelve-rayed animals with pronounced radial symmetry. Very beautifully painted, lead a sedentary lifestyle, crawl along the bottom.
- Sea lilies are sedentary beautiful animals that have the shape of a radial flower. They can separate from the substrate and move to more food-rich places.
Lifestyle can be both mobile and attached (sea lilies). The body is a two-layer, oral opening performs the function of anal and genital. The outer skeleton is quite durable, calcareous, beautifully decorated with colored patterns.
The larvae of these animals have bilateral body symmetry, and only adults grow the rays to radiality.
Combs
More often 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 oldest. Grebneviki predators eat crustaceans, small fish and even each other. They reproduce very intensively.
In the body structure, a third germinal leaf appears . The oral opening on the upper part of the body leads a free-floating lifestyle. The most common types are:
- beroe;
- platikenides;
- gastrodes;
- venerein belt;
- bolinopsis;
- t'yalfiella.
Their radial symmetry, as well as the radiation symmetry of some intestinal cavity species, is weakly expressed. The body shape resembles a bag or oval.
Generalization
Thus, the radiation symmetry of the body is the prerogative of aquatic animals leading a sedentary or attached lifestyle and giving its owners a number of advantages in hunting for prey and evading predators.