 Double cone (biology)

Double cones (DCs), known as twin cones when the two members are the same, are two cone cells (colour detecting photoreceptors) joined together that may also be coupled optically/electrically.They are the most common type of cone cells in fish, reptiles, birds, and monotremes such as the platypus and are present in most vertebrates, though they have been noted as absent in most placental mammals (including humans), elasmobranches and catfish.