Coelom is reduced to haemocoelic channels in

Options

A. Polychaeta
B. Oligochaeta
C. Hirudinea
D. Arachiannelida.

Answer

To solve the question "Coelom is reduced to haemocoelic channels in?", we will follow these steps:

### Step 1: Understand the Terms
- **Coelom**: A coelom is a fluid-filled body cavity that is completely lined by mesoderm. It is found in many animals and serves various functions, including housing organs and allowing for their movement.
- **Haemocoel**: A haemocoel is a type of body cavity that is not lined by mesoderm and is filled with blood. It is essentially a reduced form of the coelom and is typically found in certain invertebrates.

### Step 2: Analyze the Options
- **Option 1: Polyketa**: These are marine worms that possess a true coelom.
- **Option 2: Oligoketa**: These are also segmented worms (like earthworms) that have a true coelom.
- **Option 3: Hirudinia**: This class includes leeches, which have a reduced coelom that is transformed into a haemocoel.
- **Option 4: Arachinida**: This group includes arachnids (like spiders and scorpions), which have a true coelom.

### Step 3: Identify the Correct Answer
From the analysis, we can see that:
- **Hirudinia** (leeches) is the only option where the coelom is reduced to haemocoelic channels. The other options (Polyketa, Oligoketa, and Arachinida) have a true coelom.

### Conclusion
The correct answer is **Option 3: Hirudinia**.

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