What is the Difference Between Sessile and Motile?

The terms sessile and motile are used to describe the ability of organisms to move. The key difference between sessile and motile organisms lies in their mobility:

• Sessile organisms are those that cannot move and are attached to a substrate throughout their life. Examples of sessile organisms include corals, anemones, sponges, and some plants. Most sessile organisms have a radial symmetry and are passive feeders, meaning they rely on their environment to bring food to them.
• Motile organisms are those that can move independently using metabolic energy. Examples of motile organisms include fish, dolphins, and most animals. Motile organisms typically have a bilateral symmetry and are active feeders, meaning they actively seek and capture their food.

Some key differences between sessile and motile organisms include:

1. Mobility: Sessile organisms are immobile, while motile organisms can move from one place to another.
2. Attachment: Sessile organisms are attached to a substrate, while motile organisms are not.
3. Symmetry: Sessile organisms usually have radial symmetry, while motile organisms typically have bilateral symmetry.
4. Mode of Feeding: Sessile organisms are passive feeders, while motile organisms are active feeders.

Although sessile organisms are predominantly immobile, they can move via external forces such as water currents. Additionally, some sessile animals have a motile phase in their development, like sponges, which have a motile larval stage and become sessile at maturity.

Comparative Table: Sessile vs Motile

Here is a table comparing the differences between sessile and motile organisms:

Sessile organisms are species that are fixed in one place and attached to a surface, such as corals and anemones. In contrast, motile organisms are species that can move out of their fixed position and possess organs and energy generation for movement. Motile organisms can be found in various environments, including terrestrial, transitional, and marine habitats, and may live in benthic and planktonic habitats. Sampling methods for sessile organisms typically involve random quadrat sampling to estimate population size, while motile organisms may require different sampling methods depending on the organism and environment.