Question

1. which animals have well - defined skeletons and backbones?

echinoderms
arthropods
vertebrates
invertebrates

Explanation:

• Echinoderms: They have a unique internal skeleton made of calcium carbonate plates, but no backbone.
• Arthropods: They have an exoskeleton (external skeleton) made of chitin, but no backbone.
• Vertebrates: By definition, vertebrates have a well - defined internal skeleton (including a backbone made of vertebrae).
• Invertebrates: This is a broad group that lacks a backbone.

Answer:

C. vertebrates