Select the invertebrate.

 - lionfish
 - penguin
 - julia butterfly
 - grizzly bear
A lionfish is a fish. Like other fish, a lionfish is a vertebrate. It has a backbone.
A penguin is a bird. Like other birds, a penguin is a vertebrate. It has a backbone.
A grizzly bear is a mammal. Like other mammals, a grizzly bear is a vertebrate. It has a backbone.
A julia butterfly is an insect. Like other insects, a julia butterfly is an invertebrate. It does not have a backbone. It has an exoskeleton.