The animal kingdom is large and diverse. Scientists discover new species all the time, and they need a way to classify them. The science of classification is called taxonomy. In taxonomy, every kingdom of life (plant, animal, fungus, etc) branches into smaller groups called phyla. Each phylum branches into classes, and so on down to species. The presence or absence of a backbone is one of the first traits that scientists use to classify animals. Animals without a backbone are invertebrates. There are many phyla of invertebrates. Earthworms, spiders, jellyfish, starfish and butterflies are all examples of invertebrate animals. Animals with a backbone are vertebrates.

Which of these is an example of an invertebrate?

A
an oak tree, which is a kind of plant
B
a mushroom, which is a kind of fungus
C
a bat, which is an animal with a backbone
D
a snail, which is an animal without a backbone