What is ray symmetry? Which animals have radiation symmetry?

What kind of animals are not found on our planet! Some amaze with their size, someone surprises with habits and lifestyle, others are characterized by incredible coloring.

But the most striking in the structure of the body are still marine and oceanic inhabitants. Their body shape can be very unusual, since it has a special symmetry, uncharacteristic for terrestrial animals. This is the ray symmetry.

Types of body symmetry in animals

All animals by types of symmetry of the body can be divided into four groups:

• Animals with bilateral symmetry (bilateral symmetrical). This group includes most species of terrestrial animals and a significant part of marine animals. The main feature is the arrangement of the organs of the body symmetrically relative to one plane through it. For example, the left and right parts of the body, the back and front.
• Radial symmetry of the body (ray symmetry). It is typical for animals of marine and oceanic 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, with respect to which the body parts will be located symmetrically. For example, the rays of sea stars.
• Animals with an asymmetric body shape. When symmetry is not characteristic at all, the form is constantly changing depending on the environmental conditions or the movement of the animal. A typical example is amoeba vulgaris.
• Absence of symmetry completely. Such organisms include sponges. They lead an attached way of life, they can expand along the substrate to different volumes and have absolutely no symmetry in the structure of the body.

Each listed group of organisms extracts for themselves a certain benefit from their structure. Thus, for example, bilateral animals can move freely freely, turning to the sides. Animals with radial symmetry are able to catch prey from different sides. Asymmetric organisms are convenient to move around and adapt to environmental conditions.

Radial symmetry: what is it

The main distinguishing feature of animals possessing radial symmetry is their unusual body shape. They are usually dome-shaped, cylindrical or in the form of a star or ball.

Through the body of such organisms it is possible to carry out many axes, with respect to each of them there are two perfectly symmetrical halves. Such adaptation gives them the opportunity to have a number of advantages:

1. They move freely in any direction, controlling all sides around themselves.
2. Hunting takes on a larger scale, as production is felt around the whole body.
3. The unusual shape of the body allows you to adapt to the surrounding landscape, pour into it and become invisible.

Radial symmetry of the body is one of the main adaptations for certain classes of animals of the oceanic biocenosis.

Characteristic 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 the Intestinal. They led a completely sedentary, immobile lifestyle and were attached to the substrate. Such symmetry was advantageous to them, and they gave it a start.

The fact that now many actively swimming animals still have ray symmetry, speaks of its non-reduction in the course of evolution. However, this feature does not fulfill its intended purpose.

The value of the ray symmetry

Its main purpose in ancestral forms, as well as in modern, leading an attached way of life is to provide protection from predator attacks and subsistence.

After all, animals with radiation symmetry, could not protect themselves, running away from the predator, could not hide. Therefore, the only option for protection was to feel the approach of danger from either side of the body and respond in time to protective mechanisms.

In addition, it is quite difficult to get your own food when you are sedentary. And the radial symmetry allows you to catch the smallest sources of food around the whole body and quickly respond to them.

Thus, the ray symmetry of the body gives the extremely important mechanisms of self-defense and sustenance for the 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 layers, allows a person to admire the intricacy of nature and the beauty of the underwater world.

Which animals have radiation symmetry? For example, such as:

• Sea urchins;
• Jellyfish;
• Holothuria;
• Ophiuroids;
• Snake-tailings;
• Hydra;
• sea stars;
• Ctenophores;
• Immovable polyps;
• Some types of sponges.

These are the most common examples of the radiation symmetry of the body in animals. There are other animals, little-studied, and, perhaps, and still not yet open, for which this characteristic physique is characteristic.

Coelenterates

This type of animal includes three main classes, the common feature of which is that they are all animals with ray symmetry. In life cycles, either the free-swimming jellyfish stage or the stage of the polyp attached to the substrate predominates. The hole is one, it performs the function of the oral, anal and genital. For protection use poisonous stinging cells.

1. Hydroid. The main representatives: hydras, hydrants. They lead an attached way of life, have, like all coelenterates, two layers in the structure of the body: ectoderm and endoderm. The median layer is a gelatinous substance of a watery composition - mesogloe. The body shape is often goblet. The main part of life passes in the polyp stage.
2. Medusa (Scyphoid). The main representatives are all kinds of jellyfish. The shape of the body is unusual, in the form of a bell or dome. They are also two-layered animals with radiation symmetry. The main part of life passes in the stage of a freely moving jellyfish.
3. Corals (polyps). The main representatives: anemones, corals. The main feature is the colonial way of life. Many corals form whole reefs from their colonial colonies. Single forms also occur, these are different kinds of actinia. The jellyfish stage is not typical for these animals, only the stage of polyps.

In total, there are approximately 9,000 species of this type of animal.

Echinoderms

What other animals have radiation symmetry? Of course, everyone is famous and very beautiful, unusual and bright echinoderms. This type counts about 7 thousand species of these amazing species of marine fauna. There are five main classes:

• Holothurians - reminiscent of worms, but still have ray symmetry. Brightly colored, move reluctantly along the seabed.
• Ophiuri - resemble sea stars, but they have higher mobility and poor coloring - white, milky and beige.
• Sea urchins - can have a regular, acicular outer skeleton, and may not have needles. The shape of the body is almost always close to spherical.
• Starfish - five, eight or twelve-pointed animals with pronounced radial symmetry. Very beautifully painted, lifestyle leads inactive, creep along the bottom.
• Sea lilies are sedentary beautiful animals, in the form of a radial flower. They can be separated from the substrate and moved to richer food places.

The way of life can be either mobile or attached (sea lilies). The body is two-layered, the oral opening serves as an anal and sexual one. The outer skeleton is strong enough, lime, beautifully decorated with colored patterns.

The larvae of these animals have bilateral symmetry of the body, and only adults grow rays to radiality.

Ctenophora

More often smaller 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. Ctenophora predators, eat crustaceans, small fishes and even each other. Reproduce very intensely.

In the structure of the body appears the third germinal leaf. Oral opening on the upper body, lead a free-floating lifestyle. The most common species are:

• Beroe;
• Platictenides;
• Gastrodes;
• Venus belt;
• Bolops;
• Gt;

Their radial symmetry, as well as the radiation symmetry of coelenterates of some species, is weakly expressed. The shape of the body resembles a sack or an oval.

Generalization

Thus, the ray symmetry of the body is the prerogative of aquatic animals that lead a sedentary or attached lifestyle and gives their owners a number of advantages in hunting prey and evading predators.