Final answer:
Pharyngeal slits in some invertebrate chordates are used to filter food out of the water that enters the mouth, and they are modified into gill supports in fishes and into components of the ear, tonsils, and thymus glands in tetrapods.
Step-by-step explanation:
Pharyngeal slits are openings in the pharynx (the region just posterior to the mouth) that extend to the outside environment. In some invertebrate chordates, the pharyngeal slits are used to filter food out of the water that enters the mouth. These slits are modified into gill supports in fishes and into components of the ear, tonsils, and thymus glands in tetrapods (land vertebrates).