The first evidence of intrinsic epidermal bioluminescence within ray‐finned fishes in the linebelly swallower Pseudoscopelus sagamianus (Chiasmodontidae)

External and histological examination of the photophores of the linebelly swallower Pseudoscopelus sagamianus reveal three epidermal layers of cells that form the light‐producing and light‐transmitting components of the photophores. Photophores among the examined photophore tracts are not significantly different in structure but the presence of mucous cells in the superficial layers of the photophore suggest continued function of the epidermal photophore in contributing to the mucous coat. This is the first evidence of intrinsic bioluminescence in primarily epidermal photophores reported in ray‐finned fishes.