Which among the following have open circulatory system?
(i) Periplaneta
(ii) Limax
(iii) Pheretima
(iv) Hydra

Options

A. (i) and (ii) only
B. (iii) and (iv) only
C. (i) and (iii) only
D. (ii) and (iv) only

Explanation

To determine which of the given organisms have an open circulatory system, we need to analyze each option based on their classification and circulatory system type.

### Step-by-Step Solution:

1. **Identify the Organisms**:
- (i) Periplaneta (Cockroach)
- (ii) Limax (Slug)
- (iii) Pheretima (Earthworm)
- (iv) Hydra

2. **Classify Each Organism**:
- Periplaneta belongs to the phylum **Arthropoda**.
- Limax belongs to the phylum **Mollusca**.
- Pheretima is an earthworm, which belongs to the phylum **Annelida**.
- Hydra belongs to the phylum **Cnidaria**.

3. **Understand Circulatory Systems**:
- **Open Circulatory System**: Blood is not confined to blood vessels; it flows freely in the body cavity. This is typical in Arthropoda and many Mollusca.
- **Closed Circulatory System**: Blood is contained within vessels. This is typical in Annelida.
- **Absence of Circulatory System**: In some organisms like Hydra, the circulatory function is performed by a gastrovascular cavity.

4. **Analyze Each Organism**:
- **Periplaneta (Cockroach)**: Has an open circulatory system (correct).
- **Limax (Slug)**: Also has an open circulatory system (correct).
- **Pheretima (Earthworm)**: Has a closed circulatory system (incorrect).
- **Hydra**: Lacks a true circulatory system; it uses a gastrovascular cavity (incorrect).

5. **Conclusion**:
- The organisms that have an open circulatory system are **Periplaneta** and **Limax**.

### Final Answer:
The organisms that have an open circulatory system are **(i) Periplaneta** and **(ii) Limax**.