What Body Symmetries Do the Sponges Possess?

Body Symmetry Basics

• Body symmetry describes the balanced distribution of body parts on a biological organism that form some type of symmetrical pattern. Most organisms display bilateral or radial symmetry. Bilateral symmetry is when body parts will match up if an organism is divided in half. For example, most butterflies display bilateral symmetry: the two sides will be nearly identical if the animal is split down the middle. Radial symmetry is found in organisms with parts that point outward like spokes on a wheel, where the animals can be cut into identical parts along more than one plane.

Asymmetry

• Asymmetry is a unique type of body symmetry wherein the body of an organism expresses no symmetry whatsoever. Sponges are typically asymmetrical. The body form of a sponge usually consists of a porous or hollow skeleton and no body cavities. They grow to accommodate their environment, which is usually the sea floor. Their bodies will adapt to the rocks or coral around them, so their bodies will usually have no definite symmetry.

Radial Symmetry

• Some sponges, including Hexactinellida, or glass sponges, will exhibit radial symmetry. Glass sponges have a lacy, tubular shape and grow in deep, cold waters. They consist of around 500 species and reach about 1 meter in height. Other partially radially symmetrical sponges are in the class Sclerospongiae, which resemble round corals.

Importance

• The asymmetrical nature of sponges is considered a primitive characteristic. It arises because sponges lack the organs that are found in most other multicellular organisms. Asymmetry is beneficial to sponges because it allows them to thrive in numerous habitats like rocky crevices and their simplistic nature allows them to easily regenerate their body material since there is no risk of losing important organs.