Fig. 1

Tunic and fin blades development in Phallusia mammillata. A–C Embryos at St. 24 (A) and St. 25 (B) that developed in their chorions, and a hatching larva (C) were stained with calcofluor white (blue) and Sytox Green (green). Maximum intensity projections from confocal z-stacks (the corresponding 3D visualizations can be found in Additional file 3: Movie S1, Additional file 4: Movie S2 and Additional file 5: Movie S3). D 3D surface rendering from a confocal z-stack of a larva stained with CBM3a-GFP (green) and DAPI (blue) (the corresponding 3D visualization can be found as Additional file 6: Movie S4). E–H Effects of temperature during development on the formation of the tunic (stained with CBM3a-GFP in green) of larvae that arose from dechorionated eggs. Although the tunic of larvae that developed at 18 °C was devoid of median and caudal fins most of the time (E), the tunic of larvae that developed at 22 °C had more frequently median fins with a normal appearance and caudal fins with a reduced size (G). Chorionated embryos systematically gave rise to larvae with well-formed median and caudal fins (F,H). I Graph representing the proportions of larvae presenting median (blue) and caudal (orange) fins at the different culture temperatures (average values with error bars denoting standard deviation). With chorion: n = 78 (3 experiments: one at 16 °C, one at 18 °C, and one at 24 °C). 18 °C without chorion: n = 141 (3 independent experiments). 24 °C without chorion: n = 123 (3 independent experiments). 22 °C without chorion: n = 195 (4 independent experiments). 16 °C, then 22 °C without chorion: n = 48 from a single experiment. Individual data values can be found in Additional file 7: Table S1. Note that although the tunic was uniformly stained by CBM3a-GFP in dechorionated larvae, the tunic staining of chorionated larvae was always less intense in the middle part. Embryos in A and B have developed in their chorions, consequently they appear rolled up. Larvae in C–H are shown in lateral views with anterior to the left and dorsal to the top. Scale bars: 50 µm