Fig. 6

Photoreceptors and gene expression profiles of molluscan and annelid larvae. Ventral views and anterior faces up. The apical (larval) photoreceptors (red) of the trochophore of the scaphopod mollusk Antalis entalis (a), the trochophore of the polyplacophoran mollusk Leptochiton asellus (b), the 72 h after fertilization old larva of the polychaete annelid Platynereis dumerilii (c), and a generalized gastropod veliger larva (d) may be homologous based on their cerebral innervation, ontogeny, location close to the apical organ (cells labeled in gray), and their molecular fingerprint. Note that the eyes of gastropod and bivalve veliger larvae have not been characterized based on their gene expression profiles. The scaphopod and polyplacophoran post-trochal photoreceptors (green) are probably homologous since they are located posterior to the prototroch in the mantle and express similar genes. Polyplacophorans possess a pair of posteriormost photoreceptors (blue) in the mantle. The latter may be homologous to scaphopod posterior most expression domains in the pavilion (posterior mantle opening) or the posterior ventral foot based on their location and gene expression profile. The adult eyes of P. dumerilii are labeled in pink