Fig. 4

F-actin dynamics during morphogenesis of the shell field. Dorsal (a–e, k–m) and lateral (f–j, n–p) views are shown. The presumptive shell field tissues in the pretrochal region becomes invaginated at 16 hpf (dashed line in g). F-actin starts to aggregate in this region at 20 hpf (arrow in d and i), which then spreads to the posttrochal region (arrows in e and j). These aggregations show “spot” patterns at 24 hpf and “circled” patterns at 36 and 48 hpf (k–m; more details are shown in q–s). Plate fields and ridges are formed in the central region at 24 hpf (k). Stars in k indicates that the seventh ridge, the seventh plate field and inner girdle field are not detectable. The inner girdle field is recognizable between the outer girdle field and the central region (in the posttrochal region) or between the outer girdle field and prototroch (in the pretrochal region) (k–p). ri, ridge; pf, plate field; ogf, outer girdle field; igf, inner girdle field; pt, prototroch. Bars represent 50 μm