Table 1.

Tetrapoda opsins and their functions. Subfamilies characterization according to [5, 12, 78] and [4]

Subfamily	Opsins	Functions
Visual opsins	RH1 RH2 OPN1sw1 OPN1sw2 OPN1lw	Rhodopsin mediates vision in dim-light whereas conopsins are responsible for colour vision. OPN1lw is sensitive to red-green or long-wavelengths, RH2 to green or middle wavelengths and two short-wave conopsins (OPN1sw2 and OPN1sw1) respond to blue-violet or violet-ultraviolet wavelengths, respectively.
Non-visual opsins (sensu stricto)	OPN3 TMT TMT2	TMT (teleost-multiple-tissue) are expressed in the liver, kidney and heart as well as eye and brain. Phylogenetic analysis reveals that it clades with OPN3, which also exhibits a multiple patterns of tissue expression.
Pineal opsins	PARA PARIE PIN VA	Multiple opsins (PARA, PARIE, PIN) have been isolated from the parapineal complex. VA opsin is also expressed in the retina and was shown that forms a functional photopigment sensitive in the 460–480 nm range.
Photoisomerases and Neuropsins	OPN5 RGR RRH	RGR and RRH have a probable role as all-trans retinal photoisomerases. OPN5 shows an absorption maximum at 380 nm and is thus UV-sensitive.
Melanopsins	OPN4x OPN4m	Melanopsins are involved in circadian rhythm regulation and pupillary light reflexes.