Marine animal first excrete

Options

A. Ammonia
B. Urea
C. Uric acid
D. Amino acid

Answer

### Step-by-Step Solution:

1. **Understanding Excretion in Aquatic Animals**:
- Aquatic animals primarily excrete ammonia due to its high toxicity. Ammonia is soluble in water and requires a large volume of water for its excretion.

2. **Marine Environment**:
- Marine animals live in a salty environment where the concentration of salt in the surrounding water is higher than that in their body fluids.

3. **Osmosis in Marine Animals**:
- Due to the higher concentration of salt in the seawater, water tends to move out of the marine animals' bodies through a process called exosmosis. This leads to a loss of water from their bodies.

4. **Maintaining Osmolarity**:
- To counteract the loss of water and maintain osmolarity (the balance of solutes in their body fluids), marine animals need to retain some water.

5. **Excretion Process**:
- Instead of excreting ammonia, marine animals convert ammonia into urea, which is less toxic and requires less water for excretion. This adaptation allows them to conserve water while still removing waste.

6. **Classification of Marine Animals**:
- Marine animals that excrete urea are classified as ureotelic organisms. This means that they primarily excrete urea instead of ammonia or uric acid.

7. **Conclusion**:
- Therefore, the correct answer to the question of what marine animals first excrete is **urea**.