Which is not true ?

Options

A. Molluscans are shelled animals
B. Mammals have 4 chambered heart due no hair
C. Intestinal parasite , Common Roundworm , has three lips
D. External ears are absent in snakes but fangs may occur.

Answer

To determine which statement is not true, we will analyze each option provided in the question:

1. **Molluscans are shelled animals.**
- This statement is true. Molluscs, which include snails, clams, and octopuses, typically have shells that serve as protective exoskeletons.

2. **Mammals have a four-chambered heart.**
- This statement is also true. All mammals possess a four-chambered heart, which consists of two atria and two ventricles, allowing for efficient separation of oxygenated and deoxygenated blood.

3. **The intestinal parasite common roundworm has three lips.**
- This statement is true. The common roundworm, Ascaris, is known to have three anterior lips that help it attach to the intestinal wall.

4. **External ears are absent in snakes, but fangs may occur.**
- This statement is true. Snakes do not have external ears; instead, they have internal structures for hearing. However, many snakes do possess fangs, which are specialized teeth.

After analyzing all the statements, we find that all of them are true. However, the question asks for the statement that is "not true." Since the video transcript indicates that the correct option is "mammals have a four-chambered heart," it seems there might be a misunderstanding in the context of the question.

### Step-by-Step Solution:
1. **Identify the statements provided.**
- List the four statements regarding molluscans, mammals, roundworms, and snakes.

2. **Evaluate the truthfulness of each statement.**
- Assess each statement based on biological facts:
- Molluscans are shelled animals: True
- Mammals have a four-chambered heart: True
- Common roundworm has three lips: True
- Snakes lack external ears but may have fangs: True

3. **Determine which statement is not true.**
- Since all statements are true, we conclude that there is no false statement among the options provided.

4. **Clarify the confusion.**
- The video transcript suggests that the answer is "mammals have four-chambered heart," but this is actually true. Therefore, the question may have been misinterpreted.

### Conclusion:
All statements provided in the question are true. There is no statement that is "not true."