The tentacles are always solid, containing an axis of endoderm-cells resembling notochordal tissue or plantparenchyma, and are but moderately flexible.
The skeleton is cartilaginous, and the skull is remarkable for the very elongate suspensorium of the lower jaw; the tail remains in the notochordal condition, no cartilages being formed in this organ, which is destined to disappear with the gills.
Meanwhile appear at the sides of the axial notochordal tract, the mesoblastic somites.
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