Early evolution of vertebrate photoreception: lessons from lampreys and lungfishes

The southern hemisphere lamprey and the Australian lungfish possess five and four types of photoreceptors, respectively.

• Both species are considered living fossils, providing insights into early vertebrate evolution.
• The retinae are not primitive; each species has specialized photoreceptors with spectral filters for light tuning.
• G. australis has five cone-like receptor types, while N. forsteri has four cone types and one rod type.
• Each receptor type contains distinct visual pigments that are sensitive to different parts of the electromagnetic spectrum.
• This arrangement may enable G. australis to achieve pentachromatic color vision and N. forsteri to achieve tetrachromatic color vision.

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