In Sea Cucumber, the side in contact with substratum is

Options

A. Anal
B. Oral
C. Lengthwise ventral
D. None of the above.

Answer

To determine which side of the sea cucumber is in contact with the substratum, we can analyze the options given:

1. **Anal**: The anal side is located at the posterior end of the sea cucumber. Since this side does not face the substratum, this option is incorrect.

2. **Oral**: The oral side is at the anterior end of the sea cucumber. This side also does not come into contact with the substratum, making this option incorrect as well.

3. **Lengthwise**: This option refers to the orientation of the sea cucumber. However, it does not specify which side is in contact with the substratum.

4. **Ventral**: The ventral side of the sea cucumber is the underside that rests on the substratum. This is the correct answer as it is the side that makes contact with the ground.

5. **None of the above**: Since we have identified the ventral side as the correct answer, this option is also incorrect.

Thus, the side in contact with the substratum in a sea cucumber is the **lengthwise ventral** side.

### Step-by-Step Solution:
1. Identify the sides of the sea cucumber: anal, oral, lengthwise, and ventral.
2. Analyze the anal side: it is at the posterior end and does not face the substratum.
3. Analyze the oral side: it is at the anterior end and also does not face the substratum.
4. Consider the lengthwise option: it describes orientation but does not specify which side is in contact.
5. Analyze the ventral side: it is the underside that rests on the substratum.
6. Conclude that the correct answer is the **lengthwise ventral** side.