The correct option is
C. snail.
Explanation of the Correct Answer
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Definition of Arthropods: Arthropods are a diverse group of invertebrate animals characterized by their exoskeleton, segmented bodies, and jointed appendages. This group includes insects, arachnids, crustaceans, and myriapods.
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Characteristics of Arthropods:
- Exoskeleton: Made of chitin, which provides protection and support.
- Segmented Body: The body is divided into segments, which can be specialized for different functions.
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Jointed Appendages: Limbs that are jointed, allowing for a wide range of movement.
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Analysis of Each Option:
- A. Crab: Crabs are crustaceans, a subgroup of arthropods. They have a hard exoskeleton, segmented bodies, and jointed legs, fitting all the criteria for arthropods.
- B. Spider: Spiders belong to the class Arachnida, which is also part of the arthropod phylum. They have eight legs, a segmented body, and an exoskeleton, making them true arthropods.
- C. Snail: Snails are mollusks, not arthropods. They have a soft body, often protected by a hard shell, and do not possess jointed appendages or an exoskeleton made of chitin. Instead, their body is covered by a mantle, and they have a muscular foot for movement.
- D. Millipede: Millipedes are myriapods, which are a class within the arthropod phylum. They have segmented bodies and jointed legs, fitting the definition of arthropods.
Why the Other Options Are Incorrect
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A. Crab: As mentioned, crabs are crustaceans and fit all the characteristics of arthropods. They have a hard exoskeleton, jointed limbs, and a segmented body.
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B. Spider: Spiders are arachnids, another class of arthropods. They possess the defining features of arthropods, including an exoskeleton and jointed appendages.
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D. Millipede: Millipedes are classified as myriapods, which are also part of the arthropod phylum. They have a segmented body and jointed legs, making them true arthropods.
Common Pitfalls
- Confusing Mollusks with Arthropods: Students often confuse snails (mollusks) with arthropods due to their presence in similar habitats. Remember that mollusks have soft bodies and do not have jointed appendages.
- Overlooking the Characteristics: It’s essential to remember the defining characteristics of arthropods (exoskeleton, segmented body, jointed appendages) when identifying them.
Revision Summary
- Arthropods are characterized by an exoskeleton, segmented bodies, and jointed appendages.
- Crabs, spiders, and millipedes are all arthropods, while snails are mollusks.
- Understanding the classification of animals is crucial for distinguishing between different groups.
- Always check for the defining features of arthropods when answering related questions.