Figure 4

Embryogenesis of Prionchulus sp. a-l, cleavage, gastrulation and blastopore formation. Yellow, alimentary tract precursor(s); blue, slit-like blastopore; dotted circle, position of P5 (out of focus); green dot, primary POC; red arrowhead, orientation of cleavage spindle; black bars connect sister cells; m, cell lineage with seven somatic lineage branches and a germline (P0-P5); white arrowheads, asymmetric divisions; n-q and r-u, 3-D reconstructions of two embryos; p-q, t-u, differences in cell numbers (lower left corner) intentionally to visualize +/- bilateral symmetry in descendants of S4-S5 and to a lesser degree also of S3 in contrast to variable spatial arrangements of S1 and S2 descendants. Sister cells marked with white bars. Each sphere represents a nucleus; color code as shown in m. Scale bar, 10 μm.