Developmental series of embryo images, including polarized microscopy.

<p>Developmental stages and skeletal development of <i>S. neumayeri</i> under elevated pCO₂. A–C) Representative embryos at 2 cell, 16 cell and morula stages reared under ambient (unmanipulated seawater) conditions in a separate culture. D–F) Eight day old early gastrula with vegetal plate indentation where CaCO₃ spicule nuclei are first visible. Three spicule nuclei are visible under polarized light (D) from the ventral view of the embryo grown in the control treatment. Polarized (E) and brightfield (F) side views of a gastrula grown in 730 µatm pCO₂ treatment. Two spicule nuclei among the mesenchyme cells are visible from this angle. G–I) Ten day old mid-gastrula embryos (also G-inset) from three treatments: control (G), 510 µatm (H) and 730 µatm (I). Triradiate spicules are similar in shape. J–L) Twelve day old late gastrula stage embryos in three treatments. Large well-developed spicules are visible from the side (J, L) and ventral view (K). Aberrant spicule development is readily distinguishable in some individuals in the 730 µatm treatment (L).