Fig. 3

Larval development under SEM. Dorsal and lateral views are shown, with the anterior to the top. In early larvae (a–c, f–h), no differentiation of dorsal cells could be observed. For larvae after 16 hpf, panels c’–e’, h’–j’, k’–r’ show the details of pretrochal and posttrochal regions. Note that for some stages they are not the same larvae as those in c–e, h–j, k–r. The pretrochal region of the shell field is indicated by arrows in d–e and k–n. The small pore in the cells adjacent to the prototroch are highlighted by the arrowhead in k’. In larvae after 24 hpf, alternative bulges and grooves are discernable (indicated by numbers in l–n). Outer girdle field (ogf) and inner girdle field (igf) exhibit different morphological characters after 36 hpf, and are indicated by brown and green shadows, respectively (m’, n’, q’ and r’). lc, lateral cilia; pt, prototroch. Bars represent 50 μm