Vertebrate or Invertebrate?

This is a snail. It is a mammal because it drinks its mother’s milk when it is a baby. It's an vertebrate.

This is a dolphin. It is not a mammal because it doesn't drink its mother’s milk when it is a baby. It's a vertebrate.

This is a slug. It is not a mammal because it doesn't drink its mother’s milk when it is a baby. It's an invertebrate.

This is a Komodo dragon. It is not a mammal because it doesn't drink its mother’s milk when it is a baby. It's a vertebrate.

This is a starfish. It is not a mammal because it doesn't drink its mother’s milk when it is a baby. It's an invertebrate.

This is a stingray. It is not a mammal because it doesn't drink its mother’s milk when it is a baby. It's a vertebrate.