Which term describes animals without a backbone?

• A. Invertebrate
• B. Vertebrate
• C. Mollusca
• D. Echinoderm

Answer: (A)

Recognizing how animals are classified by structure, the key idea here is whether an animal has a backbone. Animals that lack a vertebral column are described by the broad term invertebrate. This label covers a huge diversity of creatures across many groups—everything from insects and spiders to snails and clams, and even starfish and sea urchins. Vertebrates, on the other hand, do have a backbone, so that term describes the opposite group. The other options point to specific groups or phyla (Mollusca for mollusks like snails and clams, Echinoderm for starfish and sea urchins). While those groups are indeed invertebrates, the question asks for the general term for animals without a backbone, which is invertebrate.