Which statement is true for molluscs?

Options

A. These have a soft body surrounded by silica shell.
B. Body is covered with external skeleton made of chitin.
C. Molluses have organ system grade of body organization with bilateral symmetry.
D. They are oviparous with direct development.

Answer

To determine which statement is true for molluscs, let's analyze the characteristics of this group of animals step by step.

### Step-by-Step Solution:

1. **Identify the Habitat**:
- Molluscs are primarily found in aquatic environments, although some can also be terrestrial. This is a general characteristic of molluscs.

2. **Examine the Body Structure**:
- Molluscs have a soft body that is typically covered by a shell. This shell is primarily made of calcium carbonate, not silica. Therefore, any statement suggesting that their shell is made of silica is incorrect.

3. **Check the Composition of the Shell**:
- The shell of molluscs is not made of chitin; instead, it is composed of calcium carbonate. Chitin is found in the exoskeletons of arthropods, not in molluscs.

4. **Analyze the Body Organization**:
- Molluscs exhibit organ system grade of body organization. They have a well-developed digestive system, nervous system, and respiratory system. This indicates a higher level of complexity in their body organization.

5. **Symmetry**:
- Molluscs display bilateral symmetry, meaning their body can be divided into two equal halves along one plane. This characteristic is true for most molluscs.

6. **Reproductive Characteristics**:
- Molluscs are generally oviparous, meaning they lay eggs. However, they do not undergo direct development; instead, they typically have a larval stage before maturing into adults. Therefore, any statement claiming they have direct development is incorrect.

### Conclusion:
Based on the analysis, the statement that is true for molluscs is: **"Mollusca has organ system grade of body organization with bilateral symmetry."**