Tentacles: from octopus to alien - From zero to sixty (legs, that is)

Putting the science in fiction - Dan Koboldt, Chuck Wendig 2018

Tentacles: from octopus to alien
From zero to sixty (legs, that is)

by Danna Staaf

Nothing says “alien” like a face full of tentacles. These appendages seem to enjoy perennial popularity in science fiction, from the Martians of H.G. Wells’s The War of the Worlds to the heptapods in the 2016 film Arrival.

The original inspiration for all these boneless limbs comes from our own home ocean. Step into the water off any coast and you’ll find it chock-full of tentacles—decorated with suction cups, stinging cells, feather dusters, and more. Writers who leave the depths of tentacular possibility unplumbed run the risk of using them as generic squiggles, slapped on a creature merely to enhance its weirdness. Here’s a bit of real-world biology to boost your creativity without getting your feet wet.

The true tentacle masters

Octopuses, squid, and cuttlefish are arguably the closest to intelligent aliens we’ve got right here on our own planet. They might even be the reason we’re prone to imagining tentacled extraterrestrials. But here’s a funny bit of trivia: Octopuses do not have tentacles. Technically.

Along with their cousins, squid and cuttlefish, octopuses belong to a group known as cephalopods, and scientists find it useful to distinguish between cephalopod “arms” and “tentacles.” Arms are shorter; tentacles are longer—and elastic. Arms are lined with suckers; tentacles only have suckers at their tips. According to these definitions, squid and cuttlefish have eight arms and two tentacles. Octopuses have eight arms and zero tentacles. And now you know.

Cephalopods can solve puzzles, use tools, play, and communicate with one another. Individuals even have distinct personalities. Yet all this complex behavior, in some ways so similar to that of our own species, is coordinated by an extremely different nervous system. Instead of one large central brain like ours, cephalopods have both a central brain and a great deal of distributed processing throughout their bodies—especially in the arms and tentacles.

As philosopher of science Peter Godfrey-Smith wrote in his book Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness (Farrar, Straus and Giroux, 2016):

“For an octopus, its arms are partly self—they can be directed and used to manipulate things. But from the central brain’s perspective, they are partly non-self too, partly agents of their own.” He goes on to explain that, “If you were an octopus … to some extent you would guide your arms, and to some extent you would just watch them go.”

Then Godfrey-Smith offers this careful caveat: “To tell the story this way is to tell it from the vantage point of the ’central octopus.’ That might be an error.” What a beautiful invitation to a fiction writer! How would you write a character whose intelligence resides throughout its limbs? Does its life feel like a continuous out-of-body experience? An in-someone-else’s-body experience?

Cephalopod arms not only exert control over their own movement, but also take in their own sensory impressions of the surrounding environment. Acting as combination finger-tongues, they are constantly touching and tasting the water, the rocks, their prey, even their fellow octopuses. Gathering sensory input like this is actually quite common for all kinds of tentacles throughout the animal kingdom. Two of the tentacles that wave shyly from the head of a garden snail are equipped with eyes, while the other two perceive chemical data. A tentacle, then, can be far more than an appendage—it can be a way of bringing the senses that, in humans, are limited to a flat face out into the world.

Remember the aliens on the planet Ixchel from Madeleine L’Engle’s A Wrinkle in Time (Farrar, Straus and Giroux, 1962)? “They had four arms and far more than five fingers to each hand, and the fingers were not fingers, but long waving tentacles … in place of ears and hair there were more tentacles.” These tentacles seemed to serve as both sense organs and the aliens’ mode of communication, producing a voice for conversation as well as transcendently beautiful song.

L’Engle did not delve into acoustic details, but I always liked to imagine that the fine hairs covering the beasts’ tentacles (and the rest of their bodies) contributed to sound production. Which brings me to the rich realm of tentacle accessories …

Accessorize, accessorize!

Cephalopod suction cups may be the best-known tentacle tack-on. In addition to their facility with touching and tasting, they can grip. There may be hundreds of suction cups on a single arm and each one can independently attach and release, facilitating delicate manipulation of objects. When acting in concert, their power is impressive. An octopus clinging to a rock is typically stronger than any diver trying to pull it off. (Note: don’t try to pull octopuses off rocks. They don’t like it. Plus, you’ll probably tear their skin. They really don’t like that.)

However, even the strongest cephalopod tentacle can’t squeeze you to death. It may be tempting to deploy a villainous octopus like eight boa constrictors to squeeze the life out of some poor victim, but cephalopod arms just don’t work that way. Their job is to stick, not constrict; during a hunt they bring prey to the mouth for killing and carving.

If you’d like to hurt someone (fictional, of course) with actual tentacles, turn from cephalopods to the marvelous world of jellyfish. Jellyfish tentacles carry loads of tiny stinging cells, and inside each one is a coiled thread ending in a minute, harpoon-like barb. When the cell is triggered, the thread inverts explosively and flings the barb into the jelly’s prey. Being punctured with a tiny barb doesn’t hurt much—the damage is done by the subsequent injection through the barb of mysterious toxins. Scientists are only beginning to understand the enormous diversity of chemicals found in jellyfish venoms, despite their potency. The world’s fiercest tentacles belong to the box jelly, whose sting is powerful enough to take down a grown human. Need an obscure or oddly specific poison? Try mining jellyfish.

Similar stinging cells are found in jellyfish relatives like coral and anemones. But if you brush the tentacles of a tide pool anemone, they’ll simply feel sticky, even though you’re experiencing an explosion of barbs similar to a jellyfish sting. To a little shrimp or fish, it might be quite painful, but to a human the sting is so mild it just feels like touching a glue stick.

Because nature is like that, there are tentacles that produce genuine glue—they just don’t belong to anemones. They belong instead to animals called comb jellies. Comb jelly tentacles are also lined with tiny cells, but instead of barbs and toxins these cells contain sticky threads that can be flung out to capture prey. They’re a bit like spiderwebs, although … maybe you can guess where I’m going with this. Of course there are tentacles that are much more like spiderwebs.

If you think you know worms because you’ve dug up earthworms, think again. Their marine cousins are (dare I say it?) a whole different can of worms. And among these, the spaghetti worm is truly exceptional. It lives in a tube of its own making, hidden in the rocks, exposing only its tentacles—but these can reach up to three feet in length. The slender, sprawling strands collect small particles of food and carry them back to the worm’s mouth. Meanwhile, they also make the surrounding reef or tide pool look like the morning after a wild party, with fallen streamers splayed every which way.

Other marine worms use a more orderly array of tentacles to capture edible bits and pieces from the surrounding water. Feather duster worms and Christmas tree worms live in tubes, too, but instead of flopping their tentacles all over the ground, they extend their tentacles upward in graceful crowns and spirals. These delicate frills may be the world’s most beautiful tentacles.

If some tentacles are so lovely we name them after holiday decorations, well, others aren’t.

The tentacles we must not name

I can hardly close any discussion of tentacles without mentioning Cthulhu. The Great Old One of H.P. Lovecraft’s imagination bore “an octopus-like head whose face was a mass of feelers.” It seems that replacing facial features with tentacles is an excellent shortcut to producing horror. Even Meg Murry in A Wrinkle in Time was initially repulsed by the aliens of Ixchel, only relaxing when the tentacles themselves began to soothe her.

Whether your tentacled creatures will ultimately prove diabolical or benevolent, it’s worth considering what seems to be humanity’s gut reaction to these appendages: to freak out. In many stories, the monsters themselves consider it, and use technology, magic, or superpowers to adopt the trope known as “A Form You Are Comfortable With.”

Consider the true forms of the Thermians in the 1999 movie Galaxy Quest. Having spent considerable screen time as humans (albeit super awkward humans), a few of these aliens abruptly show up as disturbing crosses between Cthulhu and Jabba the Hutt. It turns out they forgot to activate their “appearance generators” and quickly remedy this mistake, to the immense relief of the human protagonists.

The next time you’re working on science fiction aliens or fantasy monsters, take a moment to consider the myriad forms of tentacles right here on our own planet. Some are sticky; some are poisonous. Some bear hooks; others have eyes. Many can regenerate, and some might even think for themselves. The more we inspire ourselves with reality, the wilder the products of our own imaginations.