Which of the following is NOT considered an invertebrate?

The distinction of invertebrates is characterized by the absence of a backbone or vertebral column. Spiders, earthworms, and insects are all classified within the invertebrate category.

Crabs, however, also fall under invertebrates as they belong to the group called arthropods, which include creatures with exoskeletons and jointed limbs. The confusion might arise because crabs have a hard shell and exhibit characteristics that make them seem more complex, but they are still fundamentally invertebrates due to their lack of a backbone.

Understanding the classification of these organisms aids in appreciating the diversity of life forms and their biological structures. Each group plays a significant role in their respective ecosystems, so recognizing which creatures are invertebrates helps in proper identification and study in areas such as pest management and ecology.