At first blush, the Hawaiian bobtail squid looks like just another bioluminescent cephalopod. Like many of its relatives, the bobtail squid makes deft use of its light-emitting photophores to hunt, communicate with its peers, and hide from predators lurking below. But it's a fraud.
Instead of producing the light itself, the squid relies on a bioluminescent bacterium that dwells within its photophores. In exchange for shelter and a stable source of nutrients, the bacteria provide the squid with the ability to make light.
The relationship begins immediately at birth. After emerging from its egg, the juvenile bobtail squid acquires the bacteria from the environment, and they start the process of colonizing its developing light organs.
Studies have shown that the squid can even control the intensity of the luminescence produced by the bacteria in order to match that of the downwelling light in the water column.