So far, you have learned about classification & characterization of a number of living organisms. Well if you are confused a bit, I am talking about my articles that I have written previously on these topics.

Here we will look more closely into chordates & hemichordates. You have assured certain marks in AIPMT if you read this carefully.

Before moving towards chordates, let me talk about half chordates. What are they?

Well yes, they are hemichordates. They are categorized as a separate phylum under non chordates.  They are the sister group of echinodermates.   They mainly include tongue worms. There are approximately 90 species of hemichordates. They can be as small as in millimeters or as large as in meters (balanoglossus). They are exclusively marine. Now let me tell you some of the features of hemichordates.

  • They feed on fine particles in marine water.
  • Body cavity is true coelomic.
  • Circulatory system is partially open.
  • Body consists of three sections color, trunk & proboscis.
  • It consists of 3 classes viz. Enteropneust, Pterobranchia & Planctosphaeroidea.
  • Body is bilaterally symmetrical.
  • They are triploblastic.
  • Complete digestive system is present.
  • They respire through numerous numbers of gill slits which are present throughout body surface.
  • They show metamorphosis & involve toronaria larva in their life cycle. Larva shows mobility with the help of ciliated body.
  • Hemichordates do not have any central nervous system. Nerve tissues are concentrated in color region. It is linked with outer covering of the body i.e. Epidermis.
  • They are present on outer surface of rocks & shells which can easily be overlooked.

Some of the examples are shown here:


Let’s talk about chordates now.

Chordates are the organisms which have the backbone. There are about 48,000 species.  Take a look to its classification first.


3Let me tell you about its subphylum.

  • Cephalochordates – They are marine & filter feeder. They are small eel like organisms. They have all typical chordate features. Their dorsal nerve cord is supported by notochord. 100s of gill slits are present in pharynx which helps in food & water filtration.
    • Cephalochordates have poorly developed sense organs. Finding fossil record of them will be a hard thing as they do not have any hard body part.
  • Urochordata – They are marine, sessile & filter feeders. Some are planktonic & some are colonial. Filteration of water occurs inside the sack shaped body.
    • Urochordates also have sparse fossil record.  And they show retrogressive metamorphosis in which tadpole like larvae is involved.  Nerve cord is present in larval stage only.
    • Body of urochordates is generally covered with leathery coating which is known as tunic. Therefore, they are also known as tunicates (sea squirts).


  • Vertebrata – The classification of vertebrate is given in image below. See that carefully. Now, Let me tell you certain of the features of this category.
    • Their body is differentiated into four regions viz. head, neck, trunk & tail.
    • Degree of segmentation in their body is defined by vertebrae, ribs, nerves & muscles etc.
    • Striated muscles are attached to the outer side of skeleton.
    • Exoskeleton is made up of keratinized cells.
    • Endoskeleton is made up of bones and cartilage. It consists of living cells.
    • Spacious true coelom is also present in vertebrates.
    • Complete digestive system is present in vertebrate.
    • Fewer gill slits are present in lower aquatic organisms.
    • They usually have a pair of kidneys for excretion.
    • Anterior brain & posterior spinal cord are the parts of nervous system.
    • Numerous numbers of sense organs are also present.
    • Their brain is stored in cranium
    • All vertebrates have a heart & closed circulatory system.
    • Normally sexual & gonochoristic (unisexual) reproduction occur.


Well Guys! Thank you for showing patience. I am expecting everything is clear to you. In case if any query strikes your mind, please post it here

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I guess I should mention myself also 🙂 I am Anjali Ahuja, your biology educator.  We (askIITians + me) always try to do something good for students. We have created fascinating & interesting study material for you guys.

You are most welcome to jump in here for finding the study material.

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