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What role does the endostyle play in chordates?
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Chordate
X-ray fish (Pristella maxillaris), is an example of a chordate with a visible backbone.
In chordates, the endostyle serves two primary functions related to feeding and endocrine regulation:
- Feeding: Located on the floor of the pharynx, the endostyle is a glandular structure that secretes a sheet of mucus. In suspension-feeding chordates, this mucus moves upward along the gill slits to trap food particles suspended in the water current, which are then transported to the intestine for digestion.12
- Endocrine Function: The endostyle is the evolutionary precursor to the vertebrate thyroid gland. It possesses the specialized capacity to concentrate iodide and bind it to glycoproteins to produce thyroid hormones. In protochordates and the larvae of primitive vertebrates like lampreys, this process occurs within the endostyle. During the metamorphosis of lampreys, the endostyle breaks down, and its cells differentiate into the follicles of the thyroid gland.34
While the endostyle's role in mucus production is well-documented, the specific physiological function of the hormones it produces in certain organisms, such as lancelets, remains a subject of ongoing study.4