Which of the following organisms is closest to being isosmotic to its environment?

Options

A. Marine bony fish
B. Freshwater bony fish
C. Marine jelly fish
D. Freshwater protozoan

Explanation

To determine which organism is closest to being isosmotic to its environment, we need to understand the concept of isosmotic conditions.

### Step-by-Step Solution:

1. **Define Isosmotic**:
- Isosmotic refers to a condition where two solutions have the same osmotic pressure. This means that the concentration of solutes is equal in both solutions, leading to no net movement of water across a semipermeable membrane.

2. **Identify Osmoconformers**:
- Organisms that are isoosmotic with their environment are often referred to as osmoconformers. These organisms maintain an internal environment that is in equilibrium with the external environment.

3. **Consider Marine Organisms**:
- Most marine invertebrates are osmoconformers. They have body fluids that are isotonic with seawater, which allows them to survive in their saline environment without expending energy to regulate their internal osmotic pressure.

4. **Example of an Osmoconformer**:
- Marine jellyfish are a prime example of osmoconformers. Their internal osmotic pressure is very similar to that of the seawater they inhabit, making them isosmotic to their environment.

5. **Conclusion**:
- Based on the understanding of osmoconformers and the specific example of marine jellyfish, we conclude that marine jellyfish are the organisms that are closest to being isosmotic to their environment.

### Final Answer:
Marine jellyfish are closest to being isosmotic to their environment.

---