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What is Cephalization?

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The Cephalization - Definition, Advantages, Examples and In Arthropods

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Cephalization in zoology refers to the evolutionary trend of concentrating nervous tissue, the mouth, and sense organs toward the front end of an animal. Fully cephalized organisms have a head and brain, whereas less cephalized animals have one or more nervous tissue regions. Cephalization is associated with bilateral symmetry and forward head movement.

Bilateria: Cephalization is a distinguishing feature of the Bilateria, a large group that includes the vast majority of animal phyla. These have the capacity to move using muscles and a body plan with a front end that encounters stimuli first as the animal begins to move and has evolved to contain many of the body's sense organs, able to detect light, chemicals, and sometimes sound. A collection of nerve fibres capable of processing information from these sense organs is often present, forming a brain in some phyla and one or more ganglia in others.

Acoela: Acoela are a type of basal bilaterian that belongs to the Xenacoelomorpha. They are small and simple animals with slightly more nerve cells at the head end than anywhere else, resulting in the absence of a unique and compact brain. This is a very early stage of cephalization.

Flatworms: Platyhelminthes (flatworms) have a more complex nervous system than Acoela and are lightly cephalized, with an eyespot above the brain near the front end, for example.


Advantages in Cephalization Animals

Cephalization provides three benefits to an organism-

For starters, it promotes brain development. The brain serves as a command and control center for organizing and controlling sensory information. Animals can evolve complex neural systems and higher intelligence over time. 

The second benefit of cephalization is that sense organs can be concentrated in the front of the body. This allows a forward-facing organism to scan its environment more efficiently, allowing it to find food and shelter while avoiding predators and other dangers. As the organism moves forward, the front end of the animal senses stimuli first.

Third, cephalization moves the mouth closer to the sense organs and brain. As a result, an animal can quickly analyze food sources. Predators frequently use special sense organs near the oral cavity to gather information about prey when vision and hearing are insufficient. Cats, for example, have vibrissae (whiskers) that detect prey in the dark and when it is too close to see.

Sharks have ampullae of Lorenzini electroreceptors that allow them to map prey location.


Examples of Cephalization in Animals

Vertebrates, arthropods, and cephalopod molluscs are three groups of animals with a high degree of cephalization. 

Humans, snakes, and birds are examples of vertebrates. Lobsters, ants, and spiders are examples of arthropods. Octopuses, squid, and cuttlefish are examples of cephalopods. 

These three groups of animals have bilateral symmetry, forward movement, and well-developed brains. These three groups of species are thought to be the most intelligent on the planet.

Many more animals do not have true brains but do have cerebral ganglia. While the "head" is less clearly defined, the creature's front and back are easy to identify. The sense organs or sensory tissue, as well as the mouth or oral cavity, are located near the front. The cluster of nervous tissue, sense organs, and mouth moves to the front as a result of locomotion. While these animals' nervous systems are less centralized, associative learning still occurs. Organisms with a lower degree of cephalization include snails, flatworms, and nematodes.


Animals Without Cephalization

Cephalization does not benefit free-floating or sessile organisms. Radial symmetry is found in many aquatic species. 

Echinoderms (starfish, sea urchins, and sea cucumbers) and cnidarians are two examples (corals, anemones, jellyfish). Animals that can't move or are affected by currents must be able to find food and defend themselves against threats coming from all directions. The majority of introductory textbooks classify these animals as acephalgic or lacking cephalization. 

While none of these creatures has a brain or central nervous system, their neural tissue is organized in such a way that they can experience rapid muscular excitation and sensory processing. Nerve nets have been discovered in these creatures by modern invertebrate zoologists.


Cephalization in Arthropods

Cephalization progressed in arthropods with increasing incorporation of trunk segments into the head region. This was beneficial because it allowed for the evolution of more efficient mouth-parts for capturing and processing food. 

Insect brains are strongly cephalized, with three fused ganglia attached to the ventral nerve cord, which has a pair of ganglia in each segment of the thorax and abdomen. The insect head is a complex structure composed of several segments that are rigidly fused together and equipped with both simple and compound eyes, as well as multiple appendages such as sensory antennae and complex mouthparts (maxillae and mandibles).


Platyhelminthes Cephalization

Planarians (Class Turbellaria), tapeworms (Class Cestoda), and flukes are all members of the Phylum Platyhelminthes (flatworms) (Class Trematoda). Planarians are free-living flatworms that are completely harmless. They live in water (freshwater or saltwater) or on moist soil. Tapeworms and flukes are both internal parasites that live in the tissues, cavities in body organs, or blood vessels of their hosts.

Animals in the Phylum Platyhelminthes have bilateral symmetry, as opposed to those in the Phylum Cnidaria, which have radial symmetry. This implies that there is only one plane of symmetry (one way you can slice the animal in half and produce two pieces that are mirror images of one another).

It also means that you can tell the difference between the animal's anterior and posterior, right and left, and dorsal and ventral halves. A bilaterally symmetrical animal moves forward with its anterior and crawls on its ventral surface with its dorsal surface upward.

Members of the Phylum Platyhelminthes (particularly planarians, Class Turbellaria) have brain and sense organs in front of the animal. This is known as cephalization. The sense organs are the first to make contact with the environment in cephalized animals.


Mollusca Cephalization

Molluscs are another group that has lost and regained cephalization. Bivalves, for example, are not particularly cephalized (although some scientists have argued that they are "all head"). Certain molluscs, like the echinoderms, regained cephalization. The appropriately named cephalopods (the group that includes the squid and octopus) are distinguished by a high degree of cephalization. Their sense organs, which include well-developed eyes and a brain, are concentrated in a specific head region.


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Make notes of everything that you read. The human mind tends to forget things. To avoid forgetting stuff and strengthen the memory power of the students, revision notes should be given some emphasis.

Always approach the subject or topic through the syllabus and the previous year question paper. The syllabus gives you a bird’s eye view of what is going to be in the exam, and on the other hand, looking at the previous year question paper will tell what likely the examiner can ask in the exams. So it is easier to be precise when it comes to learning.

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FAQs on Cephalization

1. What is the Meaning of Cephalization?

Cephalization is the concentration of sense organs, nervous control, and so on at the anterior end of the body, resulting in the formation of a head and brain, both during evolution and during embryonic development.

2. Are Sponges Cephalized?

Sponges lack symmetry; they are neither radially nor bilaterally symmetric. Cephalization occurs only in animals that are bilaterally symmetrical. The cavity in the body. The body cavity is where the digestive and other internal organs develop.

3. How to download the Cephalization - Definition, Advantages, Examples and In Arthropods article?

The students can download the Cephalization - Definition, Advantages, Examples and In Arthropods article from the Vedantu’s website. There is no need for any prior registration or sign-ups to download the article. It is a great initiative by Vedantu whereby the students can have access to high-quality content free of cost from the comfort of their house. Do not miss the opportunity and download the PDF now.

4.  How to prevent getting covid-19 when going for a writing examination?

Cold-19 is a real threat to mankind today. Millions of people are losing their lives every day and thus the students need to follow all the necessary SOPs to prevent themselves from getting the covid-19 virus. The student must make sure that she is wearing a mask all the time from the beginning to the end of the examinations. Students shall always carry a hand sanitiser and use it every time they touch anything touched by all or shake hands with anyone.

5. How to build focus to study for a longer duration of time?

Developing a good focus takes time. It is not a one-day thing but something that is achieved through regular and consistent practice. To develop a good focus one should meditate every day. One can start from 10 minutes a day and further take it to 30 min or beyond. However, students should also eliminate the factors that distrust focus or consistency while studying. These elements are mobile phones, not having a proper studying plan, staying disorganized or not staying acquainted with your challenges.

6. How does learning hobbies help a student?

Hobbies are indeed one’s best friend. These could range from playing outdoor sport to playing indoor sport or other creative activities like painting or making crafts.  During the preparation phase, there are times when life feels so monotonous and tiring. In this case, hobbies act as a perfect tool to re-energise ourselves and put ourselves back on track.  Therefore, one must learn new hobbies to excel not only in studies but also in life.  One can also use a lot of free of cost content on Vedantu’s website to fuel their curiosity and build a hobby out of it.

7. What is the right way to study for the exams?

Although, making a good strategy is a question of his/her capabilities but there are certain points one shall remember to carve out the most suitable.  To begin with, always read the syllabus. The syllabus is the heart of the exam and no examiner would ever ask anything out of the syllabus. The students will get clarity and use it further to go ahead with the preparation. The students should further look at the previous year question paper, and try to solve a couple of them to understand what the examiner could exactly ask. The above-mentioned tips would help the students to approach the exam in the most right way.

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