- Pharyngeal slit
Pharyngeal slits, characteristic of both
hemichordata andchordata , are used by organisms infeeding . The wall of thepharynx is perforated by up to 200 verticalslit s, which are separated by stiffening rods.Rows of beating
cilia cause currents of water to flow through themouth , through the pharyngeal slits and out of the body through a hole in the body wall called theatriopore . 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 fish they are modified for
respiration . In tetrapods, they occur only in theembryo and disappear as development progresses. Allvertebrate s possess pharyngeal slits (and tails) in early embryonic stages, lending weight to the theory ofcommon ancestry .This is one of five hallmark characteristics that all chordates possess at some point in their life, along with the
notochord ,endostyle ,post-anal tail anddorsal hollow nerve cord .
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