http://en.wikipedia.org/wiki/Pharyngeal_slit
The presence of pharyngeal slits in hemichordates led to debates of whether this structure was homologous to the slits found in chordates or a result of convergent evolution.[8] With the placement of hemichordates and echinoderms as a sister group to chordates, a new hypothesis has emerged-suggesting that pharyngeal gill slits were present in the deuterostome ancestor .
The presence of pharyngeal slits in hemichordates led to debates of whether this structure was homologous to the slits found in chordates or a result of convergent evolution.[8] With the placement of hemichordates and echinoderms as a sister group to chordates, a new hypothesis has emerged-suggesting that pharyngeal gill slits were present in the deuterostome ancestor .
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