Fig. 3

Nuclear DAPI staining of embryogenesis in H. limbata embryos. Ventral view, anterior to the top in all panels. a–d Early embryos. a H. limbata begin ontogeny with a defined ocular region (white arrowhead) but no clear segmentation. b Segmentation remains indistinct as the germ band continues extending via the posterior elongation zone (asterisk), which is readily identifiable as a wider bulge at the posterior end of the embryo. c Segments gradually become visible in the presumptive gnathal (G, white bracket) and thoracic (T, white bracket) regions. d, e Mid stage embryos. All pre-abdominal segment borders are clearly demarcated, while abdominal segments begin developing in a sequential fashion at the extending germ band (asterisk). f, g Late stage embryos; in g, the posterior abdomen is folded laterally. Late stage embryos develop most of the 10 abdominal segments, while gnathal and thoracic limb bud development (f) and elongation (g) becomes prominent. h, i Oldest staged embryos have clearly distinguishable body segments. In younger embryos of this stage (h), segmentation is visible in the thoracic limbs (white arrow); the abdominal segments also become wider, and preliminary terminal filaments (white arrowhead) are clearly present at the posterior end of the abdomen. i Oldest embryos are notably wider throughout the anterior–posterior axis, have clearly jointed gnathal and thoracic appendages, and bear developing terminal filaments (white arrowhead). Anterior is at the top in all panels. Scale bars 0.10 mm. Image magnifications are 100X for e–h, 200X for a–d and i