Flatworms and roundworms are said to be invertebrates because?

1. Analyze the question The question asks why flatworms (Platyhelminthes) and roundworms (Nematoda) are classified as invertebrates. The answer must come from the definition of "invertebrate."

2. Explain the concept Animals are divided into two broad groups:

• Vertebrates have a backbone (vertebral column). Examples: fish, amphibians, reptiles, birds, mammals.
• Invertebrates have no backbone. Examples: worms, insects, snails, jellyfish.

The word "invertebrate" means "without vertebrae." Backbone presence or absence is the only criterion for this classification. Size, habitat, and cell number are not used.

3. Solution: checking each option

• A. They are small animals. Wrong. Size does not determine classification. Some invertebrates, like the giant squid, are very large.
• B. They can live inside vertebrates. Wrong. Many flatworms (tapeworms, liver flukes) and roundworms (Ascaris, hookworm) are parasites, but living inside a host has nothing to do with being an invertebrate.
• C. Some of them are unicellular. Wrong. Flatworms and roundworms are multicellular animals. Unicellular organisms are protozoans.
• D. They have no backbones. Correct. This is the defining feature of invertebrates.

4. Answer **D. They have no backbones.

5. Exam tip Remember: "In-vertebrate = no vertebrae." If a JAMB question asks why an animal is an invertebrate, look for the option about the absence of a backbone or vertebral column. Ignore distractors about size, habitat, or parasitism.