Fig. 6

Expression of the shell formation gene engrailed during early development of A. rubrolineata. Dorsal (a–h, k, m) and lateral (i, l, n, o) views are shown, with the anterior on the top. In lateral views (i, l, n, o), dorsal is to the right. Striped expression in the posttrochal region (ridges) is indicated by numbers (1–7). Black arrows in d–o indicate the expression in the inner girdle field that encircles the central region showing striped expression. Expression of engrailed with no evident correlation with shell field development is indicated by white crosses. Particular morphological characteristics could be recognized in the outer girdle field (gray double arrows in k–n), which should correspond to the tiny protrusions under SEM (compare to Fig. 3q’). Panels p and p’ show the engrailed expression adjacent to the prototroch, in which several positive cells right adjacent to the prototroch are highlighted by white arrows. Panel q’ corresponds to the region enclosed by the black box in q, which shows granular structures in plate fields but not in cells adjacent to the prototroch. pf, plate field; igf, inner girdle field; pt, prototroch. Bars represent 50 μm