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The notochord is a longitudinal flexible rod of cells that forms the supporting axis of the body in embryos and larvae. It is present in the midline, just ventral to the neural tube, and differentiates during the segmentation period to form large vacuolated epithelial cells and a surrounding sheath of fibrous and elastic layers. Layering of the sheath may differ in structure, thickness and development among groups; in cypriniforms there are actually three very thin layers to the sheath. A functional, well developed notochord is present throughout life in certain basal fish groups but not in cypriniforms.

ZFIN ID: ZDB-ANAT-010921-564

References: 1, 2: Kimmel et al.