Fig. 11

Scale development in A. burtoni. a Adult scales stained using Alizarin red. Scales are present in an organized arrangement, whereby their proximal-distal axis is aligned anterior-posteriorly along the trunk. Proximally, scales are overlapped by the distal part of their anterior/lateral neighboring scale(s). In the left panel, the outline of one scale is drawn using a dotted line for the proximal part that is covered by the flanking scales. In the right panel, a close up of a single scale is shown. The scales consist of concentric rings of bone, and spike elements distally, the ctenii. The scales attach to the body through their proximal end. b During development, scale Anlagen are first detected at 7 dpf, using in situ hybridization with the ossification marker collagenX, as a single row along the posterior midline (indicated “1” in the drawing to the right). At 8 dpf, one more row dorsally and one more row ventrally have appeared (indicated “2” in the drawing to the right), while the initial row has expanded anteriorly. At 9 dpf, this process has been repeated with the appearance of an additional dorsal and ventral row of scales (indicated “3” in the drawing to the right). c At 13 dpf, bone mineralization in the scales is present along the posterior trunk where they were first formed (zoom-in right panel), while more anteriorly, mineralization is still absent or less pronounced. Shown is a fluorescence image of an Alizarin red stained specimen. Abbreviations: AZR: Alizarin red; dpf: days post fertilization