The most intelligent of the invertebrates is considered to be the :

Options

A. earthworm
B. insect
C. octopus
D. spider

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the most intelligent invertebrate. To answer this, we need to analyze the intelligence levels of the given options: earthworm, insect, octopus, and spider.

2. **Analyzing Earthworm**:
- Earthworms belong to the phylum Annelida.
- They have two cerebral ganglia which function as primitive brains.
- This indicates that while they have some level of nervous system organization, their intelligence is quite basic.

3. **Analyzing Insects**:
- Insects have small brains located in their heads and additional ganglia spread throughout their bodies.
- They are capable of quick sensory responses and complex behaviors, but their intelligence is still limited compared to some other invertebrates.

4. **Analyzing Octopus**:
- Octopuses belong to the subclass Coleoidea, which includes cuttlefish and squids.
- They are known for their high intelligence, having a central brain and a small brain in each of their eight arms (totaling nine brains).
- Their nervous system is complex, allowing for advanced problem-solving and learning abilities.

5. **Analyzing Spider**:
- Spiders have very small brains, comparable in size to a poppy seed.
- Their intelligence is limited, and they primarily rely on instinctual behaviors.

6. **Conclusion**: After analyzing all the options, it is clear that the octopus stands out as the most intelligent invertebrate due to its complex nervous system and advanced cognitive abilities.

**Final Answer**: The most intelligent of the invertebrates is considered to be the **octopus**.

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