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9.1: Invertebrates

Difficulty Level: At Grade Created by: CK-12
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How are these jellyfish like an insect?

Jellyfish and insects don't seem to have much in common. They look much different. They live in very different environments. But both of these animals are classified as invertebrates.

What Are Invertebrates?

Animals are often identified as being either invertebrates or vertebrates. These are terms based on the skeletons of the animals. Vertebrates have a backbone made of bone or cartilage (cartilage is a flexible supportive tissue. You have cartilage in your ear lobes.). Invertebrates, on the other hand, have no backbone (Figure below). Invertebrates live just about anywhere. There are so many invertebrates on this planet that it is impossible to count them all. There are probably billions of billions of invertebrates. They come in many shapes and sizes, live practically anywhere and provide many services that are vital for the survival of other organisms, including us. They have been observed in the upper reaches of the atmosphere, in the driest of the deserts and in the canopies of the wettest rainforests. They can even be found in the frozen Antarctic or on the deepest parts of the ocean floor.

Snails are an example of invertebrates, animals without a backbone

Snails are an example of invertebrates, animals without a backbone.

All vertebrate organisms are in the phylum Chordata. Invertebrates, which make up about 95% (or more) of the animal kingdom, are divided into over 30 different phyla, some of which are listed below (Table below). Numerous invertebrate phyla have just a few species; some have only one described species, yet these are classified into separate phyla because of their unique characteristics. For example, sponges, with pores throughout their body, are from the phylum  Porifera. Crabs and lobsters, with jointed appendages, are from the phylum Arthropoda.

Phylum Meaning Examples
Porifera Pore bearer Sponges
Cnidaria Stinging nettle Jellyfish, corals
Platyhelminthes Flat worms Flatworms, tapeworms
Nematoda Thread like Nematodes, heartworm
Mollusca Soft Snails, clams
Annelida Little ring Earthworms, leeches
Arthropoda Jointed foot Insects, crabs
Echinodermata Spiny skin Sea stars, sea urchins


  • Invertebrates are animals without a backbone.
  • Invertebrates include insects, earthworms, jellyfish, and many other animals.

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Use the resource below to answer the questions that follow.

  1. Where do invertebrates live?
  2. What do invertebrates eat?
  3. Why are invertebrates important to the environment?
  4. What are the main invertebrate groups?


  1. What are three examples of invertebrates?
  2. How do you determine if an animal is an invertebrate?
  3. About what percent of the animal kingdom is composed of invertebrates?

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cartilage Firm tissue that provides flexible support in animal skeletons.
invertebrates Animals that lack backbones.
vertebrates Animals that have backbones of bones or cartilage.

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Difficulty Level:
At Grade
7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Aug 30, 2016
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