The term "arrow needle" is not a commonly used term in biology. It's possible that you're referring to something else, or that it's a more specific term used in a particular field of biology.

To help me understand what you're asking, could you please provide more context? For example:

* Where did you encounter this term? (e.g., a textbook, a scientific paper, a conversation)

* What was the context of the term? (e.g., was it related to a specific organism, a biological process, or a piece of equipment?)

Once I have more information, I'll be able to provide a more accurate and helpful answer.