Fig. 7

Expression of Aen-Gsx in mid-stage trochophore larvae of the scaphopod Antalis entalis. Dorsal (d)–ventral (v), anterior (a)–posterior (p), and left (l)–right (r) axes indicate the orientation. Asterisks mark the mouth opening. a Two cells (1) of the apical organ express Aen-Gsx in a 19 hpf old larva. Another two cells (2) faintly express Gsx and are located laterally to the former ones (the right cell is located in another cryotome section). b Apical view of 19 hpf old, same staged specimen showing both cells (1) in the apical organ and faintly both lateral cells 2. c Lateral view of a 21 hpf mid-stage trochophore larva. In this optical section, both Aen-Gsx-expressing cells in the apical organ and both Aen-Gsx-expressing cells (4) on both sides below the mantle lateral to the anus. d Same specimen as shown in c showing a pair of Aen-Gsx-expressing cells (3) on the latero-posterior-most side of the mantle. Both cells in the apical organ (1) as well as lateral to the latter (2) express Aen-Gsx. Inset: magnification of the Aen-Gsx-expressing cells (3) in a same staged specimen. e Same specimen as shown in c, d with both Gsx-expressing cells (4) on both sides below the mantle lateral to the anus. f This histological section shows a lateral Aen-Gsx-expressing cell (2) that penetrates the epidermis. g This histological section shows an Aen-Gsx-expressing cell (1) belonging to the apical organ. an anus, f foot, m mantle, mc mantle cavity and pt prototroch. Scale bars 50 µm