Ino-POU6 -expression during development of I. notoides . Cartoons highlight Ino-POU6-expression as black checkered domains (see Figure 1 for color-coded ganglia). Dorsal (d)-ventral (v), anterior (a)-posterior (p), and left (l)-right (r) axes indicate the orientation. (A) Ino-POU6-expression in the palliovisceral ganglia (pvg) during stage 19. Inset: Close-up of both palliovisceral ganglia. (B) Ino-POU6–expression in the pedal (pg) and palliovisceral ganglia during stage 22. (C) During stage 23 Ino-POU6 is expressed in the pedal and palliovisceral ganglia (unspecific staining around shell gland (arrowhead)). (D) Ino-POU6–expression in the pedal and palliovisceral ganglia during stage 23 (unspecific staining around shell gland (arrowhead)). (E) Vibratome section along the midline of a stage 23 individual with Ino-POU6 being expressed in the pedal and palliovisceral ganglia but not in the cerebral ganglia (cg). (F) During stage 25 Ino-POU6 is expressed in the posterior subesophageal mass (psm), the anterior basal (ab) and posterior basal lobes including the dorso-lateral (dl) and dorsal basal lobes (db) but not the optic lobes (o). (G) During stage 25 Ino-POU6 is expressed in the brain including the anterior (asm), middle (msm), and posterior subesophageal masses. (H) Ino-POU6-expression during stage 26 resembles that observed during stage 25 (vibratome section). (I) Ino-POU6-expression in the supraesophageal mass during stage 26 including the subvertical (arrowhead), the anterior basal (ab) and posterior basal lobes (pb), the inferior frontal (if), the inferior buccal (ib) and the superior buccal lobes (sb) (vibratome section). (J) During stage 27 Ino-POU6 is expressed among others in the subvertical lobe (arrowhead) and superior frontal lobe (sf). Subsequent prehatching stages cease to express Ino-POU6 in their CNS. Abbreviations: a, arm; e, eye; f, funnel; iy, internal yolk; m, mantle; og, optic ganglion; y, yolk. The statocysts are labeled by asterisks. Scale bars: A-E and I: 150 μm, F-H and J: 200 μm.