Asymmetry refers to animals that have no symmetry, which means their bodies cannot be divided into equal parts. An example of an asymmetrical animal can be found in the Phylum Porifera, which consists of sponges. Sponges are asymmetrical because tissues grow randomly and the same opening is used for breathing, eating and other digestive functions. Amoebas are also asymmetrical because they have an irregular shape and constantly change form.
Jellyfish and starfish, from the phylums Cnidaria and Echinodermata, respectively, have radial symmetry. Animals with radial symmetry are organized along a central point and can be divided into several equal parts. One way to imagine radial symmetry is to think about the spokes on a wheel, which creates several equal segments. Since animals with radial symmetry only have a top and bottom side, their sense organs are spread throughout the body. Although there is 360 degrees of sensory information, this type of symmetry results in slow movement.
Humans and other mammals, insects, reptiles, and amphibians all have bilateral symmetry. This type of symmetry occurs when an animal can be divided into two identical halves. For example; in humans, the only way to achieve bilateral symmetry is to draw a dividing line from head to toe. Bilateral symmetry creates a front and back side as well as a right and left side. A common trait among bilateral animals is cephalization, which means that sensory organs are located in a central location or the head.
Spherical symmetry is rare and, according to EncyclopediaBritannica.com, it only occurs among the protozoan groups Radiolaria and Heliozoia. To achieve spherical symmetry, the body is shaped as a ball or sphere. This symmetry creates equal halves when a line is drawn through the center from any direction. These protozoan groups are simple organisms that have no ends or sides.