The most important characteristic of phylum Porifera is that the organism

Options

A. Are cellular
B. Possess blind sac type of body plan
C. Possess canal system and choanocytes
D. Possess water vascular system

Answer

To answer the question about the most important characteristic of phylum Porifera, we can break down the information step by step.

### Step-by-Step Solution:

1. **Understanding Phylum Porifera**:
- Porifera, commonly known as sponges, are one of the simplest forms of multicellular organisms in the animal kingdom. They are primarily aquatic and are characterized by their porous bodies.

2. **Cellular Organization**:
- Organisms in this phylum are described as "cellular" or "acellular." This means they do not have true tissues or organs. Instead, they are made up of a loose aggregation of cells.

3. **Body Plan**:
- The body plan of Porifera is not organized into a blind sac. Instead, they have a unique body structure that allows them to filter water through their bodies.

4. **Canal System**:
- One of the most significant features of Porifera is their canal system. This system consists of a network of canals that facilitate the flow of water through the sponge, allowing for the exchange of nutrients and waste.

5. **Choanocytes**:
- Within this canal system, there are specialized cells called choanocytes (or collar cells). These cells have flagella that help in creating water currents, which are essential for feeding and respiration.

6. **Water Vascular System**:
- Unlike echinoderms, Porifera do not possess a water vascular system. Instead, their canal system serves a similar purpose in terms of water circulation.

7. **Conclusion**:
- Based on the characteristics discussed, the most important characteristic of phylum Porifera is that they possess a canal system and choanocytes. Therefore, the correct answer is option C.

### Final Answer:
The most important characteristic of phylum Porifera is that they **possess a canal system and choanocytes** (option C).