Additional file 2: of Reiterative use of FGF signaling in mesoderm development during embryogenesis and metamorphosis in the hemichordate Ptychodera flava

Figure S1. Development of the mesodermal structures in P. flava. (A) The presumptive endomesoderm emerges as a thickened vegetal plate (yellow and red stripes) at the late blastula stage. (B) At the mid gastrula stage, the mesodermal cells (red) are specified at the tip of the archenteron (yellow). (C) At the late gastrula stage, the mesoderm develops into the protocoel that extends dorsally and forms a duct-like structure, the hydroporic canal (black arrow), which opens in the dorsal ectoderm to form a hydropore (black asterisk). (D) After hatching, the mesoderm of the tornaria larva further differentiates into the pharyngeal muscle (green arrow) and the muscle string (black arrowhead) that reaches to the anterior ectoderm. (E) At the Spengel larval stage, the protocoel is considerably enlarged, and two paired coeloms, the mesocoels (light purple) and metacoels (dark purple), form as two pairs of rings surrounding the stomach. (F) During metamorphosis, the protocoel forms a proboscis coelom at the Agassiz stage. (G) The transforming Agassiz has a more elongated posterior region, starts losing its cilia, and is incapable of swimming. (H) The juvenile has a typical tripartite body with an anterior proboscis, followed by a collar region and a trunk. The two black dots on the anterior ectoderm indicate the eye spots. Abbreviations: prob., proboscis; col., collar. (PNG 353 kb