Figure 7 in Glide-leflection symmetly in deutelostomes: an evolutionaly pelspective

Figure 7. Scheme of a hypothetical transformation of gastrulation in deuterostomes that explains the dorsoventral inversion of some parts with retention of left–right polarity. Gastrulae are shown from left-dorso-vegetal side. A* animal pole; V* vegetal pole. Blue* ectodermal border of the blastopore whose lateral sides give rise to paired neural crests of vertebrates; yellow* embryonic area that makes the neural plate of chordates (regarded here as neurendoderm); pink* LRO distinguished by eccentric cilia; brown* notochordal area of the archenteron; grey* original floor of the archenteron. Two evolutionary steps of a single morphogenetic transformation are: animal–vegetal elongation of the blastopore over the embryonic dorsal side in basal deuterostomes* and the shift of LRO from the dorsal lip of the blastopore to the anterior tip of the archenteron in non-chordate deuterostomes* which caused the inversion of the notochordal area of archenteron from the roof to the floor. See further explanations in the text.