<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Skip Navigation
Our Terms of Use (click here to view) have changed. By continuing to use this site, you are agreeing to our new Terms of Use.

12.1: Chordates

Difficulty Level: At Grade Created by: CK-12
Atoms Practice
Estimated3 minsto complete
Practice Chordates
Estimated3 minsto complete
Practice Now
Turn In

What's a chordate?

Most chordates are animals with backbones. These range from small fish to giant whales, from playful dogs to ferocious cats. Not nearly as diverse as the invertebrates. But chordates do have many amazing species. The white tiger (Panthera tigris) is a chordate. The tiger is also from the class Mammalia, order Carnivora, and family Felidae, meaning it is a meat-eating cat.

Introduction to Chordates

The phylum Chordata consists of both invertebrate and vertebrate chordates. It is a large and diverse phylum. It includes some 60,000 species. Chordates range in length from about a centimeter to over 30 meters (100 feet). They live in marine, freshwater, terrestrial, and aerial habitats. They can be found from the equator to the poles. Several examples of chordates are pictured in Figure below.

Diversity of chordates: Tunicate, Rhinoceros, Kangaroo, Shark, Cormorant, Whale

Diversity of Chordates. These six species illustrate the diversity of the phylum Chordata.

Characteristics of Chordates

Chordates have three embryonic cell layers. They also have a segmented body with a coelom and bilateral symmetry. Chordates have a complete digestive system and a closed circulatory system. Their nervous system is centralized. There are four additional traits that are unique to chordates. These four traits, shown in Figure below, define the chordate phylum.

  1. Post-anal tail: The tail is opposite the head and extends past the anus.
  2. Dorsal hollow nerve cord: The nerve cord runs along the top, or dorsal, side of the animal. (In non chordate animals, the nerve cord is solid and runs along the bottom).
  3. Notochord: The notochord lies between the dorsal nerve cord and the digestive tract. It provides stiffness to counterbalance the pull of muscles.
  4. Pharyngeal slits: Pharyngeal slits are located in the pharynx. The pharynx is the tube that joins the mouth to the digestive and respiratory tracts.

Body plan of a typical chordate

Body Plan of a Typical Chordate. The body plan of a chordate includes a post-anal tail, notochord, dorsal hollow nerve cord, and pharyngeal slits.

In some chordates, all four traits persist throughout life and serve important functions. However, in many chordates, including humans, all four traits are present only during the embryonic stage. After that, some of the traits disappear or develop into other organs. For example, in humans, pharyngeal slits are present in embryos and later develop into the middle ear.

Classification of Chordates

Living species of chordates are classified into three major subphyla: Vertebrata, Urochordata, and Cephalochordata. Vertebrates are all chordates that have a backbone. The other two subphyla are invertebrate chordates that lack a backbone.




  • Chordates include vertebrates and invertebrates that have a notochord.
  • Chordates also have a post-anal tail, dorsal hollow nerve cord, and pharyngeal slits.
  • Vertebrate chordates have a backbone.


  1. What is a vertebrate?
  2. Identify the four defining traits of chordates.
  3. Adult humans lack some of the defining traits of chordates. Why are humans still classified in the chordate phylum?

    Notes/Highlights Having trouble? Report an issue.

    Color Highlighted Text Notes
    Please to create your own Highlights / Notes
    Show More


    dorsal hollow nerve cord

    A hollow cord dorsal to the notochord; later modified into the brain and spinal cord; embryonic features unique to chordates.

    pharyngeal slits

    Filter-feeding organs; at some stage of life, found in all chordates.

    post-anal tail

    A tail that is opposite the head and extends past the anus.


    Consists of all animals with a notochord, dorsal hollow nerve cord, post-anal tail, and pharyngeal slits during at least some stage of their life; includes fish, amphibians, reptiles, birds, and mammals.


    Animal with a vertebral column, or backbone.

    Image Attributions

    Show Hide Details
    Difficulty Level:
    At Grade

    Concept Nodes:

    Date Created:
    Feb 24, 2012
    Last Modified:
    Sep 04, 2016
    Save or share your relevant files like activites, homework and worksheet.
    To add resources, you must be the owner of the Modality. Click Customize to make your own copy.
    Please wait...
    Please wait...
    Image Detail
    Sizes: Medium | Original
    Add Note
    Please to create your own Highlights / Notes