SKELETON IN AMPHIOXUS
Exoskeleton is absent in Branchiostama. Endoskeleton include the notochord, gelatinous rods and plates, fin-ray boxes2 etc.
1. Notochord in Amphioxus : The notochord of Amphioxus is extending the whole length of the body along the mid-dorsal line just below the central nervous system. The notochord consists of a single longitudinal row of cells. The row of cells is enclosed by a thin, elastic membrane surrounded by a thick layer of fibrous connective tissue called the Notochordal sheath.
Its main function is to give support to the body and maintain its shape.
2. Gelatinous Rods and Plates: The gelatinous rods give support to the bars of the pharynx, oral cirri and free anterior edge of the oral-hood. The rods and plates are formed by elastic fibers.
3. Fin-ray Boxes: They give support to the dorsal and ventral fins. They contain gelatinous matter and thick connective tissue covering.