IDENTIFICATION OF PUTATIVE PHOTORECEPTOR CELLS IN THE SIPHON OF A CLAM, RUDITAPES-PHILIPPINARUM

A clam, Ruditapes philippinarum responds to light by siphonal retracti on and valve adduction. Sensitivity to light was seen widely diffused on the siphon, so attempts to identify possible photoreceptor cells we re made in the distal portion of the siphon which is most sensitive. H istological investigations by light- and electron-microscopy revealed microvilli arising from the epithelial cells of the outer and inner su rfaces of the siphon. Immunohistochemical experiments using anti-squid -rhodopsin serum in conjunction with FITC or streptavidin-biotin revea led specific binding of the anti-serum to the microvillar layer of the outer and inner epithelial cells. It is therefore suggested that the epithelial cells may contain a visual pigment in the microvilli and so function as a primitive photoreceptor.