Its name is derived from proteobacteria that are named after Ancient Greek Πρωτεύς (Proteus), an early sea god mentioned by Homer as "Old Man of the Sea", Ῥόδος (rhódon) for "rose", due to its pinkish color, and ὄψις (opsis) for "sight". Some members of the family, Homologous rhodopsin-like pigments, i.e. bacteriorhodopsin (of which there are more than 800 types) have Sensory Functions like opsins, integral for visual phototransduction. Many of these sensory functions are unknown – for example, the function of Neuropsin in the human retina. Members are known to have different absorption spectra including green and blue visible light.