The endostyle is an organ which assists lower-chordates (urochordates and cephalochordates, as well as the larvae of lampreys) in filter-feeding. This pharyngeal organ secretes mucus which utilizes cilia to coat itself. The mucus produced by the endostyle adheres to food particles that are in the water and this mixture is then passed through the pharynx of the organism and into the esophagus through the sweeping movement of the cilia. The endostyle in larval lampreys (ammocoetes) metamorphoses into the thyroid gland in adults, and is regarded as being homologous to the thyroid gland in vertebrates due to its iodine-concentrating activity. Since the endostyle is found in the three branches of chordates, it is presumed to have arisen in the common ancestor of these taxa, along with a shift to internal feeding for extracting suspended food from the water.