Snakes, dolphins, monkeys, and sparrows are vertebrates.

Ants and snails are not vertebrates, but invertebrates.

Vertebrates all have an endoskeleton and a spine on their back made up of individual vertebrae connected together. Most invertebrates do not have an endoskeleton, let alone a spine.

Snakes, dolphins, monkeys, and sparrows all have backbones and are all vertebrates.

Ants and snails have no backbones, so they are not vertebrates, but invertebrates.

Among them, ants are insect-like animals among arthropods. They have an exoskeleton outside their body but no bones inside their body. Snails don’t even have an exoskeleton and are molluscs. The shell outside the snail is not its skeleton.