Which of the following are most intelligent invertebrates.

Options

A. (a) Crustaceans such as cray fish and hermit crab
B. (b) Arachnidians like scorpions and spiders
C. (c) Cephalopods such as squids and octopus
D. (d) Echinoderms like starfish and sea urchin

Answer

To determine which invertebrates are considered the most intelligent, we can analyze the options provided based on their behavioral characteristics and cognitive abilities.

### Step-by-Step Solution:

1. **Identify the Groups of Invertebrates**:
- The question lists various groups of invertebrates, including crustaceans, arachnids, cephalopods, and echinoderms.

2. **Evaluate Crustaceans**:
- Crustaceans, such as crabs and lobsters, are not typically recognized for high intelligence based on their behavioral activities. Therefore, they are not the answer.

3. **Evaluate Arachnids**:
- Arachnids, which include scorpions and spiders, exhibit some intelligent behaviors. For example, certain spiders demonstrate complex hunting strategies and can engage in betrayal for survival. However, they are not considered the most intelligent invertebrates.

4. **Evaluate Cephalopods**:
- Cephalopods, such as squids and octopuses, are widely regarded as the most intelligent invertebrates. They possess several advanced cognitive abilities, including:
- A large brain-to-body ratio.
- A complex nervous system.
- Skills in spatial learning and navigation.
- Advanced predatory techniques and cooperative hunting behaviors.

5. **Evaluate Echinoderms**:
- Echinoderms, like starfish and sea urchins, are not known for intelligence and do not exhibit complex behaviors that would classify them as intelligent.

6. **Conclusion**:
- Based on the analysis, cephalopods are the most intelligent invertebrates due to their advanced cognitive abilities and complex behaviors.

### Final Answer:
The most intelligent invertebrates are **cephalopods** (such as squids and octopuses).

---