Developmental expression of the GATA456a gene in Themiste lageniformis. (A, B, E, H, J, L) Lateral views with ventral side to the left and anterior 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 showing GATA456a expression (black arrow) in the endoderm, which straddles prototrochal (bracket) and posterior posttrochal regions. (B-D) Lateral, dorsal and anterior views, respectively, of the same embryo. GATA456a expression (black arrows) is positioned toward the dorsal side of the embryo, internal to the stomodeum (white arrows). (E-G) Lateral, ventral and anterior views, respectively, of the same embryo during the initial stages of posterior elongation. GATA456a (black arrows) is expressed internally, surrounded by large prototroch cells (brackets) and dorsal to the stomodeum (white arrows). (H, I) Lateral and ventral views, respectively, during transition to the pelagosphera larva. GATA456a is expressed in the posterior trunk (black arrows) and the putative hindgut region (white arrowhead). (J) Lateral view of a crawling-stage pelagosphera. GATA456a is expressed in the midgut endoderm (black arrows). White arrowhead marks the position of the future rectum and anus. (K) Ventral view of the same larva as in (J), showing GATA456a expression is centralized (black arrow) along the A/P axis. (L) Swimming-stage pelagosphera. The expression of GATA456a is expressed in endoderm of the anterior (short black arrow) and descending curve of the intestine (long black arrow). A white arrowhead marks the position of the future anus. Asterisk marks position of the stomodeum. Brackets outline the position of large prototroch cells.