Cuttlefish Can Hypnotize Prey With Flickering Light.

Sepia officinalis is not a fish. It is a cephalopod, more closely related to octopuses and squid than to anything with a backbone, and it may be the most visually sophisticated animal in the ocean. The skin contains up to 10 million chromatophores, iridophores, and papillae per square centimeter, controlled by the nervous system with a precision that allows the cuttlefish to produce moving patterns across its entire body surface simultaneously.

The hunting behavior that uses this system most dramatically is called the passing cloud display. When a cuttlefish approaches prey, typically a crab or shrimp, it produces a rippling wave of dark and light bands that travels continuously across its body from front to back. The prey, which has visual systems tuned to detect movement, appears to become disoriented or transfixed by the display. The cuttlefish closes the distance while the prey holds still, then strikes with two feeding tentacles that extend at speeds too fast for the human eye to follow.

Whether the display genuinely hypnotizes prey in any neurological sense is debated. What is not debated is that it works. Cuttlefish using the passing cloud display have significantly higher hunting success rates than those approaching prey without it, and the display is deployed selectively, used more frequently against prey species that are more likely to flee.

The Polarized Light Channel

Cuttlefish are colorblind, which creates an apparent paradox given the sophistication of their color-changing skin. The resolution to the paradox is that cuttlefish communicate through polarized light, a channel that their eyes can detect but that most of their predators cannot.

The iridophore layer of cuttlefish skin reflects polarized light in patterns that are invisible to fish and most other predators but clearly visible to other cuttlefish. This gives cuttlefish a private communication channel, a way of signaling to each other that eavesdroppers cannot intercept. Males have been observed displaying one pattern on the side of their body facing a rival male, signaling aggression, while simultaneously displaying a different pattern on the side facing a female, signaling courtship. Two messages, sent simultaneously, to two different audiences, through two different visual channels.

Memory and the Short Life

Cuttlefish have demonstrated episodic-like memory in laboratory tests, remembering not just what they ate but where they ate it and when, and using this information to make foraging decisions. An old cuttlefish that is protein-deprived will travel to locations where it previously found protein-rich prey, while a well-fed individual will not bother. The memory is specific, located, and time-stamped.

This cognitive capacity is packed into an animal that lives for one to two years. Cuttlefish are semelparous, reproducing once and dying shortly after. Everything the cuttlefish learns, every hunting technique refined, every social strategy developed, disappears with the individual. There is no cultural transmission, no learning from parents. The sophistication is rebuilt from scratch in every generation.

That fact alone makes the cuttlefish one of the more thought-provoking animals in the ocean. The intelligence is real. The lifespan that contains it is very short.