Research on skeleton system of Thunnus tonggol

In order to reveal the bone morphology of Thunnus tonggol, we studied its skeletal system by X-ray fluoroscopy imaging and manufacturing technique of bone specimen. It is found that the skeleton of T. tonggol consists of appendicular skeleton and axial skeleton. Its appendicular skeleton includes belt bone and branched fin bone, and the axial skeleton consists of skull, spine and coccyx. The cranial skeleton of T. tonggol consists of neurocranium and splanchnocranium. The neurocranium is divided into ethmoidale, frontale, sphenoid and occipitale. The splanchnocranium is surrounded by the bones at the front of the digestive tube, and it includes arcus mandibularis, arcus hyoideus, arcus branchialis and opercular bones. The spine of T. tonggol is composed of 39 vertebraes, and the neural spine and haemal spine of the 35^th–38^th centrum deformed into epural and hypural. The 39^th centrum evolved into the urostyle. The study on skeletal system of T. tonggol not only enriches the biological basis of the genus Tunas, but also provides references for its classification and evolution.