Expression of Gva-ParaHox in the pretorsional larval stage. (A) SEM of pretorsional veliger larva. (B) High magnification of SEM of velar area showing the apical tufts and sensory cups. (C) High magnification of SEM of ciliated cells of the apical organ. (D-F) Gva-Gsx transcripts are detected in the area of the apical ganglion (grey arrow heads), in the mouth opening (yellow arrow heads), and in the ventral part of the forming digestive gland in the left side of the visceral mass (blue arrow heads). E and F are histological sections of larvae. (F) is highly magnified expression of Gva-Gsx in paired ciliary cells of the apical tuft. (G-J) Gva-Xlox is expressed in the ventral part of the digestive gland on the left side of larva: (G) and (H), blue arrow heads; and in a group of cells of the ventral neuroectoderm on the right side of the larva: (I) and (J), black arrow heads. The black rectangular area marked in (I) is shown in higher magnification in (J). (K-L) Gva-Cdx is expressed weakly in the forming digestive gland. The expression intensity is greater in a few cells in the dorsal area of the visceral mass (blue arrow heads). ag apical ganglion, at apical tuft, f foot, m mantle edge, mo mouth, sc sensory cups, v velum, vm visceral mass, y yolk.