Fig. 3
From: Early embryogenesis and organogenesis in the annelid Owenia fusiformis
Gastrulation via invagination in O. fusiformis. CLSM images of early embryonic stages from a 6 hpf (beginning of gastrulation) to h 10 hpf (post gastrulation). a At 6 hpf the gastral plate starts invaginating with the 5Q macromeres at the front of the archenteron roof (b). c By 7 hpf the archenteron roof connects with the animal ectoderm (closed arrowhead) (inset), and the polar bodies have internalized into the blastocoel (c, d). e Gastrulation ends by 9 hpf, in which the two germinal layers: endoderm and ectoderm are formed; while the mesoderm precursors and chaetoblasts form at the dorso-posterior end of the embryo (g, h). Arrows in (h) show the row of presumptive prototrochal cells dividing. bl: blastocoel; bp: blastopore; cb: chaetoblast; gv: germinal vesicle; ms: mesodermal precursor cells; pb: polar bodies; vf: vegetal cross furrow. Scale bar is 50 µm