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10.2: Animal Classification

Created by: CK-12
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Plant or animal?

Animal. What type? Now that is a good question. This azure vase sponge is an animal, but how is it classified? It is estimated that there are easily over a million species of animals on Earth. How are all these species divided into their various classifications?

Classification of Animals

All animals share basic traits. But animals also show a lot of diversity. They range from simple sponges to complex humans.

Major Animal Phyla

Members of the animal kingdom are divided into more than 30 phyla. Table below lists the nine phyla with the greatest number of species. Each of the animal phyla listed in the table has at least 10,000 species.

Phylum Animals It Includes
Porifera sponges
Cnidaria jellyfish, corals
Platyhelminthes flatworms, tapeworms, flukes
Nematoda roundworms
Mollusca snails, clams, squids
Annelida earthworms, leeches, marine worms
Arthropoda insects, spiders, crustaceans, centipedes
Echinodermata sea stars, sea urchins, sand dollars, sea cucumbers
Chordata tunicates, lancelets, fish, amphibians, reptiles, birds, mammals

Invertebrate vs. Vertebrate

The first eight phyla listed in Table above include only invertebrate animals. Invertebrates are animals that lack a vertebral column, or backbone. The last phylum in the table, the Chordata, also includes many invertebrate species. Tunicates and lancelets are both invertebrates. Altogether, invertebrates make up at least 95 percent of all animal species. The remaining animals are vertebrates. Vertebrates are animals that have a backbone. All vertebrates belong to the phylum Chordata. They include fish, amphibians, reptiles, birds, and mammals.


  • Vertebrates have a backbone, but invertebrates do not.
  • Except for the chordates, all animal phyla consist only of invertebrates.
  • Chordates include both vertebrates and invertebrates.


Use this resource to answer the questions that follow.

  1. What is a vertebrate?
  2. Give examples of invertebrates.
  3. Discuss which you believe are more common, vertebrates or invertebrates?


1. State how the phylum Chordata differs from other animal phyla.

2. Compare and contrast invertebrates and vertebrates.

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Difficulty Level:

At Grade


Date Created:

Feb 24, 2012

Last Modified:

Apr 04, 2014
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