Fig. 13

Ossification of the cranio-facial skeleton in A. burtoni. At 6 dpf, ongoing ossification can be detected in the craniofacial skeleton using in situ hybridization with collagenX. This clearly visualizes the formation of the branchiostegal rays (red arrowhead), which form without a cartilage intermediate (compare 6 dpf in Fig. 12). At 9 dpf, most of the adult bones of the cranio-facial skeleton have started ossification, as shown by Alizarin red staining (fluorescence microscopy images shown), and the formation of teeth has started (orange arrowhead). Full formation of the complete opercular series (opercle, infraopercle, subopercle and preopercle) is shown for a 13 dpf specimen. Note that many bones in the skull form without a cartilaginous intermediate. Therefore, there is no one to one correspondence between the chondrogenic elements in Fig. 12 and the ossifying elements in Fig. 13. The legend in the figure indicates for which specimen each anatomical element is indicated. Abbreviations: l: lateral view; v: ventral view; f: frontal view; dpf: days post fertilization