ˌpȯ(r)fəˈräpsə̇n noun
( -s )
Etymology: Greek porphyra purple + English -opsin
: a purple pigment in the retinal rods of freshwater fishes that resembles rhodopsin both biologically and chemically and differs structurally only in having an additional double bond in the molecule and that is bleached by light to opsin and the retinene related to vitamin A 2 and is regenerated in the dark