You a head or anything else. And

You probably realize that most animals have heads. But some, including starfish, don’t. Why is having a head so important to some animals and not to others? This lesson discusses cephalization and why it’s so important.

What Is Cephalization?

If I were to ask you to name the parts of a starfish, what would you answer? Well, they obviously have five arms (sometimes more). But what else? Unless you were well versed in echinoderm anatomy, there’s a good chance you’d stop there. You may be thinking to yourself right now, wait a minute, starfish are just legs and a body! They don’t have a head or anything else.

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And you’d be right. Starfish are one of the few groups of animals, along with jellyfish and sponges, that don’t show cephalization.In the simplest sense, cephalization means having a head.

In fact, the term originates from the Greek word for head, kephale. But there’s a little more to it than that. Think about how important your head is and what it contains. Internally, it holds your brain, and externally, it has your primary sense organs (your eyes, nose, ears, and mouth).

This is the real essence of cephalization, the concentration of nervous tissue into a single, controlling organ and the organization of sense organs into one area at the anterior (head) end of the body as opposed to the posterior (tail end.)

Advantages of Cephalization

So, why does the majority of animal life show cephalization? Well, this trait holds multiple evolutionary advantages, such as the development of a brain, the concentration of the sense organs at the front of the body, and the close proximity of the mouth to the sense organs. Let’s explore each of these advantages in further detail.

Development of a Brain

An obvious advantage of cephalization is the development of a control center or brain. The brain is a concentration of nervous tissue that coordinates and controls sensory information and nervous activity. A larger brain allows for smarter and more complex animals. A more sizable brain is able to control a greater number of specialized organ systems, which leads to more sophisticated animals.

As an example, look at the flatworm, the simplest animal to show cephalization. Its very tiny brain controls eyespots, which allow the flatworm to sense light versus dark. This can’t really be considered sight, but it’s still an improvement over the jellyfish, which doesn’t have this ability. However, compare this to your advanced brain and eyes that not only have true sight, but can differentiate, by some estimates, ten million different colors.

Concentration of Sense Organs

Additionally, with cephalization, the sense organs all tend to be located on the head. Your sense organs, such as your eyes, nose, and ears, are the body parts that collect information about your environment and then send that information to the brain. Why is this important? Well, animals with heads move in the direction of their anterior end. We move straight ‘ahead,’ right? So, having the sense organs also at this end allows animals to experience and respond to their environment more efficiently.Think of it this way – it makes more sense to have your eyes viewing what’s in front of you rather than what’s behind you. Also, having the sense organs next to the brain means that sensory input doesn’t have to travel very far to be interpreted.

This allows the brain to respond to environmental changes as quickly as possible.

Mouth Located Near Sense Organs

Finally, having your mouth next to your sensory organs makes finding food much easier. Think about your cat or dog sniffing on the floor to locate the treat you left for him. This is especially important for predators who often have very little time between spotting prey and attacking and who frequently use their mouths to kill.

Additionally, having a mouth at the anterior end sets up the body to have a complete digestive tract. In other words, there is a distinct entrance and exit to the digestive tract, such as a mouth and an anus, each with their assigned roles. And, no, not all animals have this.

Lesson Summary

The majority of animal life shows cephalization, or the presence of a head at the anterior (head) end of the body. The tail end of the animal’s body is referred to as the posterior end.

There are multiple advantages to cephalization, including the development of a brain, the concentration of the sense organs at the anterior end of the body, and the close proximity of the mouth to the sense organs. A brain is a concentration of nervous tissue that coordinates and controls sensory information and nervous activity. The sense organs, such as the eyes, nose, and ears, are the body parts that collect information about the environment and then send that information to the brain.

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