Here’s a very cool organism, the vampire squid, Vampyroteuthis infernalis, from a paper by Robison et al. (2003). It’s a small deepwater predator that swims where it’s dim and dark, and where the oxygen concentrations are extremely low. Despite the fearsome name, it’s soft and weak, relying on its low metabolic rate to harvest prey in places where more active, ferocious predators can’t abide. Like many cephalopods, it has amazing visual display capabilities; in this case, because it lives in the dark, it has fluorescent tentacles.

The archaic, deep-sea cephalopod Vampyroteuthis infernalis occurs in dark, oxygen-poor waters below 600 m off Monterey Bay, California. Living specimens, collected gently with a remotely operated vehicle (ROV) and quickly transported to a laboratory ashore, have revealed two hitherto undescribed means of bioluminescent expression for the species. In the first, light is produced by a new type of organ located at the tips of all eight arms. In the second, a viscous fluid containing microscopic luminous particles is released from the arm tips to form a glowing cloud around the animal. Both modes of light production are apparently linked to anti-predation strategies. Use of the tip-lights is readily educed by contact stimuli, while fluid expulsion has a much higher triggering threshold. Coelenterazine and luciferase are the chemical precursors of light production. This paper presents observations on the structure and operation of the arm-tip light organs, the character of the luminous cloud, and how the light they produce is incorporated into behavioral patterns.

These glowing armtips can flash or glow steadily, and the animal can wave them around to produce a confusing display of weaving lights in the darkness that they can presumably use to signal conspecifics, and to confuse predators. You can see more pictures and a movie on the investigator’s website.

We’re familiar with the idea of squid and octopi spraying out a cloud of ink to distract predators; this strategy obviously wouldn’t work at all in the dark depths where Vampyroteuthis lurks. Instead, the tips of the tentacles are translucent, contain clusters of iridescent green and yellow particles, and can ooze a viscous, glowing goo. Instead of a black fog, these guys spew a sparkling, glowing cloud and flash their waving tentacle tip lights in a pattern to bewilder, and presumably swim away while their foes thrash at fluorescing ejecta.

Robison BH, Reisenbichler KR, Hunt JC, Haddock SHD (2003) Light Production by the Arm Tips of the Deep-Sea Cephalopod Vampyroteuthis infernalis. Biol. Bull. 205:102-109.