In sheer numbers and distribution, which of the following groups of animal are the most successful :

Options

A. arthropods
B. snails and clams
C. vertebrates
D. sponges

Explanation

To determine which group of animals is the most successful in terms of sheer numbers and distribution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the most successful group of animals based on their numbers and distribution across the planet.

2. **Identifying the Options**: We need to look at the options provided (though they are not listed here, we will focus on the known groups).

3. **Researching Animal Groups**: The main groups of animals to consider are:
- Arthropods
- Mollusks
- Chordates
- Annelids
- Echinoderms

4. **Analyzing the Arthropods**:
- Arthropods are the largest phylum in the animal kingdom.
- They include insects, arachnids, crustaceans, and more.
- It is estimated that there are over 1 million described species of arthropods, and they represent about 75-90% of all known living and fossil organisms.

5. **Comparing with Other Groups**:
- While other groups like mollusks and chordates are also diverse, they do not match the sheer numbers and distribution of arthropods.
- For example, insects alone (a class within arthropods) make up a significant portion of biodiversity.

6. **Conclusion**: Based on the analysis, the group of animals that is most successful in sheer numbers and distribution is the **Arthropods**.

### Final Answer:
The correct answer is **Arthropods**.

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