Figure 2.

The embryonic development of P. excavatus was staged based on its morphology. Gastrulation (GA), the embryonic stage 1–9 (E1–9), and the juvenile stage (J). Gastrulation stage is shown in ventral view. Embryos are shown with the anterior end at the left and the dorsal side at the top. Abbreviations: an, anus; bp, blastopore; cg, cerebral ganglion; ds, dissepiment; dv, dorsal vessel; gbL, left germinal band; gu, gut; mo, mouth; pe, peristomium; ph, pharynx; pr, prostomium; pv, pumping vessel; py, pygidium; se, segment; st, stomodaeum. Scale bar, 100 μm.