Final answer:
Pharyngeal slits are grooves in chordates that develop into slits opening into the pharynx. They allow for the exit of water during feeding and are modified into various structures in different vertebrates.
Step-by-step explanation:
The grooves in chordates that develop into slits that open into the pharynx are called pharyngeal slits. Pharyngeal slits are found in chordates, including humans, during the embryonic stage. They allow for the exit of water that enters the mouth during feeding in aquatic organisms and are used by some invertebrate chordates to filter food from the water. In vertebrates, pharyngeal slits are modified into gill supports in fishes, while in tetrapods (land vertebrates) they are modified into components of the ear, tonsils, and thymus glands.