Hemitergite development and <i>engrailed</i> expression in whole mount (A, C, C3) and flat mounted (all others) stage 8 embryos of <i>Strigamia maritima</i>.

<p>All images orientated with anterior to the left. Images with the same letter indicate same specimen; A, C, D, D2 and D4: fluorescent nuclear staining (Sytox Green) to show the morphology; A1, C1, D1, D3 and D5 respectively same view as A, C, D, D2 and D4, under transmitted light, showing pattern of <i>en</i> expression. <b>A–A1.</b> Lateral view of whole-mount embryo with approximately 60% hemitergite extension on the anterior region of the trunk; note the correlation between the hemitergite dorsal border (<i>htb</i>) and the extent of the <i>engrailed</i> stripe. <b>B.</b> Ventral view of posterior trunk of embryo under transmitted light; note the reduced continuous dorsoventral <i>engrailed</i> stripe corresponding to the last leg-bearing segment (<i>llb</i>) at the posterior end. <b>C–C1.</b> Oblique view of embryo showing anterior region with approximately 75% of hemitergite dorsal extension and undifferentiated dorsal epithelium (<i>ude</i>). The tracheal pits (<i>tp</i>) become more conspicuous at this stage (insert). <b>D–D1.</b> Lateral view of whole-mount embryo with 90% hemitergite extension on the anterior region; note the correlation with the extent of the <i>engrailed</i> expression stripe. The anteriormost part of the trunk lacks expression due to the presence of residual yolk during dissection (<i>dotted line</i>). <b>D2–D3.</b> Close up of developing hemitergites and limb buds (<i>lb</i>). The morphology of the intercalary furrow (<i>if</i>) has become more accentuated. <b>D4–D5.</b> Detail of hemitergites, showing the anterior and posterior tergite borders (<i>solid lines</i>) and the intercalary furrow (<i>dashed line</i>), and together creating a clear distinction between the pretergite (<i>pt</i>) and metatergite (<i>mt</i>); note that the <i>engrailed</i> expression stripe is confined to the posterior portion of the (meta)tergite. Other abbreviations: <i>an</i>, antennae; <i>mxp</i>, maxilliped; <i>pct,</i> proctodeum; <i>arrowhead</i>, undifferentiated epithelium. Scale bars: 400 µm for A, A1, D, D1; 200 µm for B, C, C1; 100 µm for D2, D3; 50 µm for D4, D5; 75 µm for insert in C.