What is the function of the pneumostome in slug respiration?

• A. It serves as the breathing pore, allowing air to enter the mantle cavity for gas exchange.
• B. It filters water for oxygen.
• C. It is used to excrete waste.
• D. It is used to sense light.

Answer: (A)

In slugs, respiration happens in a mantle cavity that acts like a simple lung. The pneumostome is the breathing pore that opens to the outside, letting air enter the mantle cavity for gas exchange. When the slug needs oxygen, it can widen the mantle cavity to draw air in through this opening, and carbon dioxide diffuses out as blood vessels in the cavity pick up O2. This opening can be opened and closed to regulate ventilation and moisture, which is important for a terrestrial lifestyle. It’s not for filtering water, removing waste, or sensing light—those functions come from other parts of the slug’s anatomy. So the pneumostome’s role is to provide the entry point for air to reach the mantle cavity for gas exchange.