Fig. 7

Chordin expression in the three species. (a-h) Expression of Flchd in three embryos of similar age, and one that is slightly older, in side (a,c,e,g) and oral views (b, d, f, h). Expression becomes more localized and then fades away as the embryo ages. C.echinata chordin shows a different early expression pattern from that seen in the other species, being expressed in the presumptive endoderm at the blastula stage, as shown in (i), which is looking down onto the developing blastopore. (j) As the presumptive endoderm sinks aborally to form the blastopore expression becomes localized to its margins, as shown in this blastoporal view. In (i, j) the center of the developing blastopore is marked with an asterisk. (k) Lateral view of a slightly older embryo showing expression in the ectodermal wall of the bowl-shaped gastrula. (l) Expression in the ectoderm of the wall continues as the embryo continues to elongate. In A.millepora, expression begins in isolated cells at the oral end surrounding the blastopore [11] before becoming localized to one side of the blastopore (m) where expression gradually intensifies. In the early planula expression is localized to a patch of ectoderm on one side toward the oral end (o). This patch of expression then becomes stronger and more restricted (p), before disappearing well before settlement