Haemocoel is found in

Options

A. Hydra and Aurelia
B. Taenia and Ascaris
C. Cockroach and scorpion
D. Balanoglossus and Herdmania

Answer

### Step-by-Step Solution

1. **Understanding the Term "Haemocoel":**
- The term "haemocoel" can be broken down into two parts: "haemo," which refers to blood, and "coel," which means cavity. Thus, haemocoel refers to a cavity in which blood is present.

2. **Characteristics of Haemocoel:**
- Haemocoel is a body cavity found in certain organisms, specifically those with an open circulatory system. In an open circulatory system, blood is not confined to blood vessels but instead flows freely within the cavity.

3. **Identifying Organisms with Haemocoel:**
- Haemocoel is primarily found in organisms belonging to the phylum Arthropoda. This includes a wide range of animals such as insects, arachnids, and crustaceans.

4. **Evaluating the Options:**
- The options given in the question include:
- Hydra
- Aurelia
- Pinea
- Ascaris
- Cockroach
- Scorpion
- Hydra and Aurelia are not part of the phylum Arthropoda. Pinea (likely a misspelling of "Pinna," a type of mollusk) and Ascaris (a nematode) also do not belong to Arthropoda.

5. **Selecting the Correct Answer:**
- The organisms that do belong to the phylum Arthropoda from the options are Cockroach and Scorpion. Both of these organisms have a haemocoel as they possess an open circulatory system.

6. **Conclusion:**
- Therefore, the correct answer to the question "Haemocoel is found in" is **Cockroach and Scorpion** (option number 3).