What do we call animals without backbones?

Animals without backbones are referred to as invertebrates. This classification includes a vast majority of animal species, making up about 95% of all known animal life. Invertebrates are characterized by their lack of a vertebral column (spine), which distinguishes them from vertebrates, the animals that possess a backbone.

This group encompasses various organisms, including insects, arachnids, mollusks, and cnidarians, among others. Invertebrates play crucial roles in ecosystems, often serving as pollinators, decomposers, and vital parts of food webs. Understanding this classification helps to illuminate the diversity of life forms and their evolutionary significance.

The other options refer to specific groups or classifications of animals. Vertebrates, for instance, include all animals with a backbone, such as mammals, birds, reptiles, and amphibians. Crustaceans are a subset of invertebrates that specifically include animals like crabs and lobsters but do not encompass all invertebrates. Mammals represent another distinct group that is characterized by traits such as fur or hair and mammary glands, yet they fall under the broader category of vertebrates.