Expression of Gva-ParaHox during trochophore larval stage. (A) SEM of a late trochophore larvae (18-24 hpf). (B-C) Gva-Gsx expression is first detected in early trochophore larva (12 hpf) in a pair of dorso-medial domains of episphere (red arrow heads). (D-K) In late trochophore larva (18-24 hpf) Gva-Gsx is expressed in the dorso-medial episphere (red arrow heads), in the apical sensory organ (grey arrow heads), and around the stomodeum (yellow arrow heads). (F) is higher magnification of Gva-Gsx expression in the apical sensory organ (the area marked by the black rectangle in E) and (H) is the higher magnification of Gva-Gsx expression around the stomodeum. (L-O) Gva-Xlox transcripts are detected in a pair of cell clusters in the ventral episphere (red arrow heads) and as a semicircle around the anal marker (black arrow heads). (P-S) Gva-Cdx is expressed in the left and right primary mesentoblasts (green arrows) and neuroectodermal cells in the hyposphere (black arrow heads). (O) and (S) are false colour images of the in situ hybridization stain, superimposed on fluorescent micrographs stained for nuclei. am anal marker, ao apical organ, f foot rudiment, n protonephridium, pt prototroch, s stomodeum, sf shell field.