Pineal and retinal photoreceptors in embryonic Rivulus marmoratus poey.

The development of pineal and retinal photoreceptors was studied in embryos of Rivulus marmoratus Poey from 0.2 to 0.7 incubation period. Photoreceptors in both these organs are developed and clearly divided into outer and inner segments at mid-incubation period, in addition retinal photoreceptors are arranged in a square mosaic. However, while retinal photoreceptors contain synaptic ribbons at this developmental stage pineal photoreceptors do not; although presynaptic electron densities are present. At 0.7 incubation period synaptic ribbons are present in basal processes of pineal photoreceptors, while those in retinal photoreceptors have lengthened. The sequence of the development of photoreceptor structure in pineal and retina is discussed.