Star Fish is able to crawl over substratum by means of
(a) Arms
(b) Spines
(c) Pedicellariae
(d) Tube feet

Options

A. Arms
B. Spines
C. Pedicellariae
D. Tube feet.

Answer

To answer the question "Star Fish is able to crawl over substratum by means of," we need to analyze the options provided:

1. **Understanding the Anatomy of Starfish**:
- Starfish, also known as Asterias, have a unique anatomy that allows them to move effectively across surfaces.

2. **Evaluating Each Option**:
- **(a) Arms**: While the arms are important for movement, they primarily serve as support and direction rather than the main mechanism for crawling.
- **(b) Spines**: Spines are present on the surface of the starfish and provide protection, but they do not play a role in locomotion.
- **(c) Pedicellariae**: These are small pincer-like structures that help in cleaning the surface of the starfish and do not contribute to movement.
- **(d) Tube feet**: These are part of the water vascular system and are crucial for locomotion. They extend and contract to allow the starfish to grip the substrate and move.

3. **Conclusion**:
- The correct answer is **(d) Tube feet**. Tube feet are essential for the crawling movement of starfish over the substratum.

### Step-by-Step Solution:
1. Identify the organism in question: Starfish (Asterias).
2. Analyze the options provided for movement mechanisms.
3. Understand the function of each structure:
- Arms: Support and direction.
- Spines: Protection.
- Pedicellariae: Cleaning.
- Tube feet: Locomotion.
4. Conclude that tube feet are the primary means by which starfish crawl over surfaces.