Pharyngeal slit

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Pharyngeal slits, found in both hemichordata and chordata, are used by organisms in feeding. The wall of the pharynx is perforated by up to 200 vertical slits, which are separated by stiffening rods.

Rows of beating cilia cause currents of water to flow through the mouth, through the pharyngeal slits and out of the body through a hole in the body wall called the atriopore. Small particles in the water are trapped by the cilia in different parts of the mouth chamber and separated into materials that the organism can eat.

In primitive chordates the pharyngeal slits are used to strain water and filter out food particles; in fishes they are modified for respiration. Most terrestrial vertebrates have pharyngeal slits only in the embryonic stage.

This is one of four hallmark characteristics that all chordates possess at some point in their life.