Chapter 11

Introduction to Invertebrates

11.1 Lesson 11.1: Overview of Animals

Lesson Objectives

• List the characteristics that define the animal kingdom.


• Define and give examples of the invertebrates.

Check Your Understanding

• What are the main differences between an animal cell and a plant cell?


• How do animals get their energy?

Introduction

How are animals different from other forms of life? Recall that all animals are eukaryotic,
meaning that they have cells with true nuclei and membrane-bound organelles. Another
feature that distinguishes animals from animal-like protists is that animals are multicellular,
while protists are often unicellular. Because animals are multicellular, animal cells can be
organized into tissues, organs, and organ systems. Finally, animals areheterotrophic,
meaning they must ingest some type of organic matter for nutrition and energy (Figure
11.1).

Eukaryotic, multicellular, and heterotrophic are features shared by all the millions of diverse
types of animals on earth, from tiny ants and snails to giant whales and grizzly bears. In
this chapter we will just focus on the invertebrates, the animals that do not have a backbone
of bone or cartilage.