The Vampire Squid lives in a world where vision works differently. No sunlight illuminates the waters that surround it. Eyesight there is a secondary sense – mostly useful in detecting sparks of bioluminescence against the enfolding blackness. The squid, and the other denizens of the deep ocean, do not get their vision of their surroundings primarily from their eyesight. They see each other by sensing the pressure waves produced by swimming bodies.
When they move, these animals push the water out of their way – producing a bow wave. Nearby swimmers detect those pressure waves with sensors on their skin. Those sensors impart a sense of the strength of the wave, and of the direction it comes from. This allows them to envision the movements around them.
The Vampire Squid’s world is unique. The water there, near the bottom, is anoxic. Fish that absorb oxygen through their gills cannot breathe there. The vampires have adapted to this predator-free environment. Foraging in that world works differently for them.
The water-column extends for a mile above them. Some of the creatures living in those waters closer to the light – larvaceans, sea angels – forage by casting a sticky web into the water around them. After harvesting what they have snared, these creatures cast off their net, which then drifts away into the darkness below. In the depths, these cast-off secretions create a constant shower of biogenic snow that continually settles from above. The vampires feed by extending a thread to which this sinking debris sticks. They feed by drawing this thread through their beaks.
These squid live near the bottom of the food chain. They can forage without moving much (which conserves on oxygen consumption). They drift on the current, producing few pressure waves – so remaining invisible to the pressure wave sensors of the predators around them.
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One set of pressure waves that sometimes arises in this environment is sound waves. These are higher frequency waves than those produced by the movement of creatures through the water. They are generated in the larynxes of predators that drop in on this deep environment from above. They see the other animals in the darkness through the acoustic calls they broadcast. Those predators illuminate their prey with sound waves, and detect them through the echoes of their sonar calls which reflect back to them.
The Vampire Squid will survive the sonic searches of such predators if it can become invisible to them by dropping out of their acoustic sight. To do that, the squid has developed a behavior to minimize its illumination by sound waves.
When it is disturbed, this creature appears to turn itself inside-out. It spreads its legs wide, and the webbing between them stretches to form a cape the squid can draw back over its entire body. The animal wraps itself completely beneath this soft, flexible sheet. This is reminiscent of Count Dracula’s trick of wrapping himself completely within his cape, prior to his disappearance (thus their name “Vampire Squid”).
The full-body wrap has the appearance of a defensive posture. The creature transforms into a rubbery ball. It looks nothing like the tail, head, and arms of a squid. It may be unrecognized by predators hunting by touch.
The surface of this wrap alters its acoustic appearance. It carries rows of flexible fingers that obscure the sonic signature of its curved outline. Its spherical shape would minimize the reflection of sound waves back toward their source. Its soft texture should absorb sound, instead of reflecting it. The transformation is well suited to minimize the animal’s acoustic detection – a defensive adaptation to predators that hunt through the darkness using sonar.
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The Vampire Squid are relicts of an ocean that flourished more than 100 milliion years ago (1). They represent the oldest of the modern cephalopod lineages. They incorporate features from both the octopi and the squid – their line predates the divergence of the modern forms. Back then, the Jurassic mosasaurs hunted the seas by sight. The ammonite nautalids were growing thick shells for defense. The vampires may have chosen those times to fade into the deeper, darker depths to avoid their predators.
The mammalian predators that search through today’s deepest oceans appeared much more recently – 25 million years ago. Then the vampire squid came under pressure to mount a further defense. The advent of their cloaking behavior may have been a response to the sonar of those mammalian predators. The capacity of the Vampire Squid to disappear behind their cape and escape from acoustic detection may have been the adaptation that allowed them to continue on into modern times.
Notes: I have described the adaptations of the modern predators of the Vampire Squid (Vampyroteuthes) in Chapter 18 “Beaked Whales” in “Between the Rocks and the Stars”.
- Uribe, J. E. & Zardaya, R. 2017 Revisiting the phylogeny of Cephalopoda using complete mitochondrial genomes. Journal of Molluscan Studies 83, 133-144