Fig. 2. Ultrastructure of rods and cones in Rhinobatos typus. (A) Typical rod (r) and cone (c) morphology. (B,C) Different types of cone photoreceptors can be distinguished based on minor differences in receptor size, mitochondrial alignment and the location of the nucleus in the outer nuclear layer. (D) High-power micrograph of the outer segment (os) of a cone photoreceptor showing the lack of a plasma membrane surrounding the discs. c, cone; cn, cone nucleus; m, mitochondria; my, myoid; r, rod. Scale bars: (A–C) 5 µm; and (D) 0.5 µm.