(A) Model of early extraembryonic tissue development in M. abdita based on marker gene expression in fixed specimen. Stage (st) and time after egg lay (AEL) are defined as in (Wotton et al., 2014); absolute time given in minutes relative to the onset of germband extension (onset GBE = 0 min). (B–D’’’) Global embryonic views of SPIM recorded embryos at corresponding stages (B–D), with tracked and marked serosa (blue), amnion (orange), and ectoderm cells (grey) in 2D-projections of indicated surface areas in dorsal (B’–B’’’) and lateral views (C’–C’’’, D’–D’’’). Cells of serosa were identified based on their ability to spread over the embryo and then tracked back to the cellular blastoderm. (E) Cell lineage and divisions in putative amnion and ectoderm cells. Cells directly adjacent to the serosa never divided and could be back-tracked to a single row of cells next to the serosa anlage; these cells were classified as presumptive amnion. Cells further distal to the serosa divided, eventually decreased in cell size, and were classified as presumptive ectoderm. (F) Quantitative analysis of cell size of tracked serosa, amnion, and ectodermal cells relative to GBE as measure of developmental progression. The position of the posterior germband is indicated in % egg length (0% EL = posterior pole; dotted line); Standard error of mean shown as shades. Unless indicated otherwise, embryos and close-ups are shown with anterior left and dorsal up. Scale bars, 10 µm.