part of tracheal section taenidial fold FBbt:00005046 A specialization of the cuticular lining of the trachea consisting of annular or helical ridges that project into the tracheal lumen (their precise pattern varies along trachea). They prevent the collapse of branches while allowing them to expand and contract along their length, like the corrugated hose of a vacuum cleaner. fly_anatomy.ontology cuticular specialization