The correct option is C. Millipede. Detailed Explanation: To understand why the millipede is the correct answer, we need to analyze the characteristics of each of the organisms listed in the options:

1. Snail (Option A):
2. Snails are mollusks and possess a soft body, which is usually protected by a hard shell.
3. They have a distinct head with tentacles (which are sensory organs) and a foot that helps them move.
4. Snails do not have chaetae (bristle-like structures), but they do have tentacles and a well-defined head with sensory organs, making them unsuitable for this question.
5. Crab (Option B):
6. Crabs are crustaceans and are characterized by their hard exoskeleton, jointed limbs, and segmented bodies.
7. They have antennae (used for sensing their environment) and do not have chaetae. However, they do have appendages that serve similar functions to tentacles, such as pincers and walking legs.
8. Therefore, crabs do not fit the criteria of lacking both tentacles and antennae.
9. Millipede (Option C):
10. Millipedes belong to the class Diplopoda and are known for their elongated bodies with many segments.
11. They do not have chaetae, which are typically found in annelids like earthworms.
12. Millipedes do not possess tentacles or antennae in the traditional sense; instead, they have simple sensory structures on their heads, but these are not the same as the tentacles found in snails or the antennae found in crabs.
13. Thus, millipedes are the only organisms in this list that lack chaetae, tentacles, and antennae.
14. Earthworm (Option D):
15. Earthworms are annelids and are characterized by their segmented bodies and the presence of chaetae, which help them move through soil.
16. They do not have tentacles or antennae, but they do have a well-developed body structure that includes chaetae.
17. Therefore, earthworms cannot be the correct answer since they possess chaetae.

Summary of Why Other Options Are Incorrect:

• Snail: Has tentacles and a head with sensory organs.
• Crab: Has antennae and appendages that function similarly to tentacles.
• Earthworm: Has chaetae, which are essential for its movement.

Common Pitfalls:

• Confusing sensory structures: Students may confuse the sensory structures of different organisms (like tentacles and antennae) and misidentify them.
• Overlooking chaetae: It's important to remember that chaetae are specific to certain groups of animals, primarily annelids.

Revision Summary:

• Millipedes lack chaetae, tentacles, and antennae, making them unique among the options.
• Snails have tentacles; crabs have antennae and similar appendages; earthworms have chaetae.
• Understanding the anatomical features of different organisms is crucial for identifying their characteristics accurately.
• Always clarify the definitions of terms like chaetae, tentacles, and antennae to avoid confusion.