Developmental expression of the GATA456b gene in Themiste lageniformis. (A, B, E, H, J, L) Lateral views with ventral side to the left, anterior is up; (C) dorsal view with anterior up; (D, G) anterior views with ventral down; (F, I, K) ventral views with anterior up. (A) Post-gastrula embryo showing GATA456b expression localized to a central patch of cells (black arrow) surrounded by the prototroch (bracket). (B-D) Lateral, dorsal and anterior views, respectively, of the same embryo. GATA456b is expressed in a patch of endoderm cells (solid black arrows) dorsal to the stomodeum (white arrows) and in discrete cells and cell clusters adjacent to the endoderm (broken black arrows). (E-G) Lateral, dorsal and anterior views, respectively, of the same embryo during the initial stages of posterior elongation. GATA456b is expressed in a central anterior domain (solid black arrows), and in cells both outside and flanking each side of the central domain (broken-black arrows). (H, I) Lateral and ventral views of the same specimen during transition to the pelagosphera. GATA456b is expressed broadly in the central posterior trunk region (black arrows). (J, K) Lateral and ventral views of the same crawling-stage pelagosphera. GATA456b is expressed in the midgut (black arrows). White arrowhead marks the position of the future rectum and anus. (L) Lateral view of a swimming-stage pelagosphera. GATA456b is transcribed in regions of the anterior (short black arrow) and descending curve of the intestine (long black arrow). White arrowhead marks position of the future anus. Asterisk marks position of the stomodeum. hour, hours; d, days. Brackets outline the anterior band of large prototroch cells.