Developmental expression of GATA456 in Chaetopterus. (A, B) Vegetal views; (D, F, G, K, M, O) lateral views, anterior to the top, ventral left; (E, I, J, L, N) ventral views, anterior to the top. (A) GATA456 expression in vegetal plate cells (arrow). (B) Expression on vegetal surface (arrow) of gastrula embryo. (C) Gastrula in (B) showing expression in surface (black arrow) and subsurface cells (white arrow). (D) Embryo at 11 hours with internal expression (arrow). (E, F) Expression in endoderm (solid black arrows), bilateral cells (broken black arrows) adjacent to endoderm and anterior dorsal cells (arrowhead). (G) Larva at 25 hours showing endodermal expression (arrow). (H) Posterior view of larva in (G) with expression in endoderm (solid black arrow) and outside the endoderm (broken black arrows). (I) Right side of 25-hour larva with GATA456 in endoderm (broken white arc) and cells (broken black arrows) flanking endoderm. (J, K) Larva at 27 hours showing expression (arrows) in midgut epithelium. (L, M) Expression is prominent in foregut-midgut (long arrow) and midgut-hindgut (short arrow) junctions. (N) Enlarged ventral view of L3. Expression in foregut-midgut junction (long black arrow), midgut epithelium (solid white arrow), and distinct pairs of lateral (broken white arrows) and medial (black arrowheads) midgut cells. (Inset) magnification of (N) showing expression in medial cells (arrowheads) and smaller surface cells (white arrow) of the midgut. (O) L3 larva with expression in foregut-midgut junction (long black arrow), ventral midgut cell (white arrow), and between midgut and hindgut compartments (short black arrow). (P) Dorsal posterior head region of L3 with GATA456 in bilateral cell patches (black arrows) adjacent to pharyngeal diverticula (white arrow). (Q) Dorsal view of foregut-midgut junction (broken white lines) showing expression on midgut side (short black arrow) and in pharyngeal valve cells (white arrows). Asterisk marks position of the stomodeum. h, hours post fertilization; at, apical tuft; hg, hindgut; mg, midgut; pyg, pygidium.