Do you know what this photo shows? Is it a strange tree branch? A cactus? Maybe a fungus? Actually, it’s an animal called a sea sponge. A sea sponge doesn’t look anything like the animals you’re probably familiar with—animals like ducks and dogs, fish and frogs. Why is a sea sponge considered an animal? What traits must an organism have to be classified in the Animal Kingdom? You’ll find out in this chapter. You’ll learn just what it means to be an animal.