Which of the following is an example of an invertebrate?

The option indicating a spider is the correct answer as it belongs to the class of animals known as invertebrates. Invertebrates are characterized by the absence of a vertebral column, or backbone. Spiders, which are arachnids, represent a significant group of invertebrates that have an exoskeleton, segmented bodies, and jointed appendages.

In contrast, dogs and birds are classified as vertebrates because they have a backbone. Dogs belong to the class Mammalia, and birds belong to Aves, both of which are part of the larger group of animals possessing a skeletal structure with a spine. Turtles also fall under the vertebrate category, as they are reptiles with a defined vertebral column. This distinction helps to categorize various animal species based on their structural characteristics, emphasizing the absence of a backbone in invertebrates, such as spiders.