How do bottle-tailed squids use glowing bacteria to produce light?

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A blue-ringed octopus with bright blue rings on its beige body crawls over a rocky, coral-strewn seabed. — cephalopod Blue-ringed octopus (genus *Hapalochlaena*).

Bottle-tailed squids (sepiolids) utilize bioluminescence through a symbiotic relationship with light-producing bacteria housed within specialized cavities on the underside of their bodies.12

Rather than producing light through their own internal biochemical reactions, these squids cultivate cultures of luminescent bacteria. When the squid emerges from the sand at night, it regulates the light emitted from these bacterial colonies by expanding or contracting the openings of the cavities. This process is responsive to the amount of moonlight penetrating the water above; by adjusting the intensity of the bacterial glow, the squid effectively masks its own silhouette, making it less visible to predators lurking below.21