The retina is a key component of the vertebrate circadian system; it is responsible for detecting and transmitting the environmental illumination conditions (day/night cycles) to the brain to synchronize the circadian clock sited in the suprachiasmatic nucleus (SCN).  For this, retinal ganglion cells (RGCs) project to the SCN and other non-visual areas. In the chicken, intrinsically photosensitive RGCs (ipRGCs) expressing the photopigment melanopsin (Opn4), transmit photic information and regulate diverse non-visual tasks. In non-mammalian vertebrates, two genes encode for Opn4: the Xenopus (Opn4x) and the mammalian (Opn4m) orthologs. Remarkably, RGCs express both Opn4 genes but are not the only inner retinal cells expressing Opn4x, since horizontal cells (HCs) also do so. Here, we further characterize primary cultures of both populations of inner retinal cells (RGCs and HCs) that express Opn4x. The expression of this non-visual photopigment as well as that for different circadian markers such as the clock genes Cry1 and Cry2 and the key melatonin synthesizing enzyme, arylalkylamine N-acetyltransferase (AA-NAT), appears very early in development in both cell populations. Results clearly suggest that non-visual Opn4 photoreceptors and endogenous clocks converge all together in these inner retinal cell populations at early developmental stages.