Bilateral symmetry is the same arrangement of parts of the body in the left and right half on both sides of the central axis or plane. Figuratively speaking, if you draw a line from the head to the tail of the body, both sides are mirror images of each other. In this case, the body exhibits bilateral symmetry, which is also known as planar symmetry, since one plane divides the body into mirror halves. We learn all about bilateral symmetry and consider some examples. We will also discuss the main advantages.
Symmetry Definition
Symmetry is associated with the orientation of the body on a plane or around an axis. Given the various forms and orientations of various organisms, scientists came up with three main types of symmetry:
- The first type is radial symmetry. With this type, the body plan is based on the axis. In other words, the body is oriented so that it is reflected due to an imaginary line through the center of the body. These organisms have top and bottom, but they do not have left and right sides, front and back. A couple of examples of radial symmetry are starfish, jellyfish, and sea anemones.
- There are some organisms that do not show symmetry at all. They are classified as asymmetric. 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 the right and left sides, which are mirror images of each other. Let's look at this type of symmetry in a bit more detail.
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 in the middle of your body, right through your nose and divide 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 two-sided symmetry. Other examples that you might not have thought of are sharks, butterflies, and ants.
Benefits of Bilateral Symmetry
Thus, there are actually some real advantages 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 led to the formation of the head and tail region. This means that everything can go in one direction and go out on the other, unlike those organisms that must use the same hole. Without going into details, let's just say that we are all very happy about this.
Another advantage is that bilateral symmetry allows the development of a more thorough nervous system that can control the body. Many animals have two-sided symmetry of the body, which means 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 arthropods is a mirror image of the left half. This is two-way 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 similar to a pie shape, where each part is almost identical, although they have no left or right sides. Instead, they have upper and lower surfaces. Organisms that exhibit radial symmetry are, for example, corals, jellyfish and sea anemones, sea urchins and starfish.
Features of Bilateral Symmetric Organisms
Organisms that have bilateral symmetry exhibit anterior and posterior, upper and lower, as well as left and right sides. As a rule, they 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 forms of life, but they develop differently as they grow.
There is one marine animal that does not show symmetry at all: sponges. These organisms are multicellular, but remain the only asymmetric animals. This means that in their bodies there is no place where you could divide them in half and see mirror images.