SYMMETRY IN ANIMALS

What is symmetry? Most animals have bodies that show symmetry. This means that the body can be cut into two halves that have a matching shape. This slide has symmetry. It has been cut into two halves that have matching shapes.

1. Asymmetrical An asymmetrical animal has no definite shape. amoeba An asymmetrical animal has no definite shape. Therefore, it can not be cut into matching halves. sponge

2. Spherical A spherical animal is shaped like a ball or a sphere. volvox

3. Radial Symmetry An animal with radial symmetry has body parts that radiate from a center point. These animals meet their environment equally from all sides. They move quite slowly. If they are sessile, their food must float by or they must create water currents. Spiny brittle star Sea anemone

4. Bilateral Symmetry dorsal Concentration of nerves and sense organs at the anterior end. Food capturing structures are usually close to the head. Digestive, excretory and reproductive structures are found closer to the posterior end. A streamline body allows for faster movement. posterior This is a shape that is two-sided and produces a mirror image effect. Right & left side Anterior end = head Posterior end = tail dorsal surface = back ventral surface = front anterior left right ventral

Which type of symmetry provides animals with the greatest chance for survival? WHY?