1. Protection from sediment: Bottom-dwelling sharks and rays often inhabit environments with fine sediments, such as sand or mud. When they are feeding or resting on the bottom, these sediments can easily enter the mouth and damage the delicate gill filaments. By being able to close the gill slits, the animal can prevent the ingestion of these sediments, protecting its gills from damage.
2. Improved camouflage: Many bottom-dwelling sharks and rays rely on camouflage to ambush prey or avoid predators. Being able to close the gill slits helps them to maintain a streamlined body shape and reduce their visibility. With its protruding gills covered, the animal can better blend in with its surroundings and remain undetected by predators or prey.
3. Enhanced buoyancy control: Some bottom-dwelling sharks and rays use their gills to help control their buoyancy. By adjusting the amount of water that enters and exits the gills, they can maintain their position in the water column without expending excessive energy. Being able to bring in the gills allows them to fine-tune their buoyancy control, making it easier to remain near the bottom or ascend and descend as needed.
4. Efficient respiration: In general, sharks and rays breathe by drawing water in through their mouths and expelling it through their gill slits. However, when a bottom-dwelling species has its mouth closed, it may still need to respire. By bringing in the gills, the animal can continue to exchange water and extract oxygen from the surrounding environment, even while its mouth is closed.