Figure 2

Mid- to late pharyngular-stage embryos of Eptatretus burgeri . (A–C) Left lateral views of 3D-reconstructed embryos at stages 45, 50, and 53. Pharyngeal endoderm is colored yellow and the arterial system is colored red. The light blue color beneath the brain primordia represents oronasal ectodermal derivatives (for details, see [10]). Note that the caudal half of the pharynx shifts caudally by the expansion of the pharyngeal arch 3 and 4 domain. (D–F) Reconstructions of embryos at stages 40, 50, and 53, with Tbx1/10A-positive mesodermal components (colored pink) as well as somites (sm). Note that somites initially arise caudal to the entire pharynx at stage 40, and later shift rostrally to reach the mid-otic level (F).