Radial symmetry is usually, echibited in animals which

Options

A. are attached to the substratum
B. Have one opening of alimentary canal
C. Live in water
D. Have ciliary mode of feeding

Explanation

### Step-by-Step Solution

1. **Understanding Radial Symmetry**: Radial symmetry refers to the arrangement of body parts around a central axis. Animals with radial symmetry can be divided into similar halves by multiple planes passing through the central axis.

2. **Identifying Characteristics of Radially Symmetrical Animals**:
- Radially symmetrical animals are often sessile, meaning they are attached to a substrate and do not move freely.
- Many of these animals have a simple body plan and may have a single opening to their digestive system.

3. **Evaluating the Options**:
- **Option A: Are attached to the substratum**: This is true for most radially symmetrical animals, as they are typically sessile.
- **Option B: Have one opening of alimentary canal**: While some radially symmetrical organisms may have a single opening, many, like adult echinoderms, have a complete digestive system. Therefore, this option is not universally applicable.
- **Option C: Live in water**: Both radially symmetrical and bilaterally symmetrical animals can live in water, making this option too broad to be definitive.
- **Option D: Have ciliary mode of feeding**: Ciliary feeding is more common in certain higher invertebrates, which are often bilaterally symmetrical, thus this option is also incorrect.

4. **Conclusion**: After evaluating all the options, the most accurate statement regarding radially symmetrical animals is that they are typically attached to a substratum. Therefore, the correct answer is **Option A**.