Which of the following is not a characteristic of sponges ?

Options

A. Sessile filter feeders
B. Body wall has two cell layers
C. Water enters through a single cavity, the osculum
D. Amoeboid cells digest food and make skeletal fibres and gametes

Explanation

To determine which of the following is not a characteristic of sponges, we will analyze each option based on the known characteristics of sponges (phylum Porifera).

### Step-by-Step Solution:

1. **Understand the Characteristics of Sponges**:
- Sponges are aquatic animals, mostly marine, and are known for their porous bodies.
- They have a cellular level of organization, meaning they consist of different types of cells but do not form true tissues.
- The body wall of sponges consists of three layers: the outer layer (pinacoderm), the middle layer (mesohyl), and the inner layer (choanoderm).
- They are sessile, meaning they are fixed in one place and do not move.
- Sponges are filter feeders, drawing water through their bodies to extract food particles.

2. **Analyze Each Option**:
- **Option A**: "Sessile filter feeders" - This is true. Sponges are indeed sessile and filter feeders.
- **Option B**: "Body wall has two cell layers" - This is also true. While sponges have three layers, the two outer layers (pinacoderm and choanoderm) are cellular, which fits the description of having two cell layers.
- **Option C**: "Water enters through a single cavity, the osculum" - This is false. Water enters through the inhalant pores (ostia) and exits through the osculum, which is the exhalant pore.
- **Option D**: "Amoeboid cells digest food and make skeletal fibers and gums" - This is true. Amoeboid cells (amoebocytes) are responsible for digestion and the secretion of skeletal materials.

3. **Conclusion**:
- The option that is not a characteristic of sponges is **Option C**: "Water enters through a single cavity, the osculum." This statement is incorrect because water enters through the ostia, not the osculum.

### Final Answer:
**Option C**: Water enters through a single cavity, the osculum.

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