part of part of immediately preceded by immediately preceded by occurrent late gastrula stage stage 19 open mouth stage early pluteus stage 2-arm stage This stage is characterized by the opening of the mouth. The right and left coelomic pouches are prominent and well-separated from the foregut by narrow coelomic constrictions. Pronounced cardiac and developing pyloric constrictions (separating respectively the foregut and midgut, and the midgut and hindgut) are visible; the gut is thus visibly tripartite. The developing stomach (former midgut) is enlarged relative to the other segments of the gut and muscle bands surrounding the esophagus are apparent. The ciliary band(s) is (are) also discernable. ecao_developmental_stage