In Amphioxus the notochord is immediately surrounded by a structureless cuticular layer, the chordal sheath.
In Elasmobranchii the chordal sheath is weak and the skeletogenous layer strong.
Of the divine spheral music, the one is the chordal harmony, the other the consecutive harmony or melody.
The notochord remains permanently unconstricted and is enclosed in a chordal sheath, external to which is the skeletogenous layer.
chordal chord·al (kôr'dl)
Of or relating to a chorda or cord.