Tentacles
Tentacles are slender, limb-like structures found on various organisms, serving multiple functions such as protection, sensory perception, and food capture. Prominently featured in coelenterates like jellyfish, anemones, and coral polyps, tentacles play a crucial role in the digestive processes of these creatures. Coelenterates possess a single body opening for both food intake and waste expulsion, surrounded by tentacles equipped with specialized stinging cells, called nematocysts, that can immobilize prey.
Certain species, such as the Australian box jellyfish, are known for their potent venom, which can pose severe risks to humans. Other marine animals, including octopuses and squid, have more developed tentacles that aid in hunting and navigating their environments. Additionally, some terrestrial animals like the star-nosed mole and caecilians utilize tentacles for sensory purposes, enhancing their ability to locate food. Overall, tentacles are integral to the survival and ecological roles of these diverse organisms in both aquatic and terrestrial ecosystems.
Tentacles
Tentacles are slender, leg-like, or arm-like protrusions from the body of a living organism. They are used for protection, as organs of touch, or to capture food. They are often seen in coelenterates, an animal phylum that includes jellyfish, anemones, and coral polyps. The name coelenterate comes from the Latin for “hollow intestine.”
Coelenterates are hollow tissue sacs with two layers of cells in their walls. The cells carry out digestion, excretion, and reproduction. There is one body opening, a mouth. Food enters it, is digested, and used by the cells. Waste also leaves through the mouth, surrounded by long, slender sense organs called tentacles, which also grab food and pull it into the mouth.
Box Jellyfish: Poison Tentacles
The Australian box jellyfish (Chironex fleckeri), also called the sea wasp, is native to Australia’s north coast and Southeast Asian coastlines. They are the largest box jellyfish species and are among Earth's most poisonous creatures. They get their name from their box-shaped, translucent bodies, approximately 1.25 feet wide. They can have up to sixty tentacles, up to 15 feet long and 0.25 inches in diameter, hanging from the box in four bundles.
The box holds an eye and a mouth. Prey—plankton, small fish, and shrimp—are caught in tentacles and pulled into the mouth. Tentacles hold huge numbers of sting cells called nematocysts. When something comes in contact with the tentacles, the nematocysts inject a poison that paralyzes and kills their prey and can cause extreme pain and even death to large animals or humans. Severe stings will kill within four to six minutes after a human is stung.
Worm and Mollusk Tentacles
Some worms have tentacles. For example, sandworms (family Nereidae) inhabit shallow ocean waters worldwide. Most live in sand or mud burrows. They have colorful bodies ranging from one inch to three feet long and are in the same phylum as earthworms. A sandworm body has several hundred segments. Each segment has two muscular parapodia, both attached to bundles of bristly chaetae. The first segment of a sandworm holds two light-sensitive tentacles, four eyes, and two sensory palps. The second segment has eight more tentacles called cirri. The palps and cirri help sandworms find crustaceans, small fish carrion, and other prey.
Many cephalopods have tentacles. For example, the nautilus (family Nautilidae) is found in the South Pacific and Indian oceans. All nautilids have soft bodies with spiral, brown, and white shells. Their mouths have beaks and radulas (toothed tongues) to eat carrion and crustaceans on ocean bottoms. Around the nautilid mouth are almost one hundred short tentacles that are used to sense objects, feed, and move. At one side of the arms, an opening called a funnel allows water to enter and carry oxygen to the gills. A nautilid can also spray a jet of water from the funnel to swim.
Octopus and Squid Tentacles
Octopuses (family Octopodidae) have eight slender, flexible tentacles. On the underside of each arm is a row of suckers. Sensors in suckers serve in defense, detect prey, capture it, and identify its texture, shape, and taste. Arms join at their bases into a bulb-shaped head/body.
An octopus squeezes water out of the mantle cavity and moves its tentacles to swim. It captures mollusk and crab prey by wrapping tentacles around them and using its suckers to tear them to pieces. In the center of the arm juncture is its mouth, which has a radula and a beak to continue shredding prey.
The giant squid (Architeuthisdux) inhabits the depths of the Atlantic Ocean. Its torpedo-shaped body is up to sixteen feet in diameter and twenty-five feet long from head to tail. This cephalopod tapers toward its posterior and has at the tail end two fins for swimming and steering. Two eyes provide excellent vision. In front of the eyes are eight round, elongated tentacles with suckers and hooks on their undersides. Two longer tentacles lack suckers and hooks, except at the tip. The tentacles are thirty-six feet long, and from tail to tentacle tip, giant squid often exceed sixty feet in length. They are Earth’s largest invertebrates. Squid hide near the ocean bottom and ambush or pursue prey. The two long tentacles are shot forward to seize their victims, which are passed along to the mouth. A beak in the mouth crushes and tears up prey.
The deep-sea squid (Grimalditeuthis bonplandi) uses its long tentacles to mimic the movements of small fish or other sea creatures, which lure in larger prey. Once the prey is close and moves in to bite the tentacle, the squid can grab it.
Squid and octopus are globally eaten by humans. Nautilids, sandworms, and related organisms help maintain the balance of nature, eating carrion and helping to keep the ocean clean. Other tentacled organisms are eaten by fish that humans use as food. On the other hand, squid and octopuses eat food, such as fish and crabs, competing with humans, and jellyfish can kill via the nematocysts in their tentacles.
Vertebrates
North America's semiaquatic star-nosed mole (Condylura cristata) has a highly sensitive nose with twenty-two pink, fleshy tentacles. Though the mole can not see well, its sensitive tentacles allow it to expertly navigate and find prey in its underground habitat. Each tentacle is covered in nerve endings called Eimer’s organs, allowing them to smell and feel their surroundings and eat prey in one-fifth of a second—the fastest of any known animal. Caecilians are the only amphibians with tentacles. They have one on either side of their head that is believed to help them smell and find food.
Principal Terms
Bud: Protuberance used in asexual reproduction
Budding: Bud development into a complete organism
Carrion: Dead animals
Funnel: An opening in a cephalopod mantle, providing oxygen and propulsion
Gamete: Sperm or an egg
Nematocyst: Poison sting cell
Radula: Tongue-like, toothed organ that grinds food and drills holes in shells of prey
Bibliography
Arnst, John. "What's the Difference between Arms and Tentacles?" Live Science, 29 Nov. 2021, www.livescience.com/difference-arms-tentacles. Accessed 25 Sept. 2024.
Benningfield, Damond. "Arms vs. Tentacles." Science and the Sea, University of Texas Marine Science Institute, 13 Aug. 2023, www.scienceandthesea.org/program/arms-vs-tentacles. Accessed 25 Sept. 2024.
Hunt, James C. Octopus and Squid. Monterey Bay Aquarium Foundation, 1997.
León, Vicki. A Tangle of Octopuses: Plus Cuttlefish, Nautiluses, and a Giant Squid or Two. Boston, Silver Burdett Press, 1999.
Williams, Peter R. Jellyfish. Reaktion Books, 2020.
Yonge, Charles M., and T. E. Thompson. Living Marine Molluscs. Collins, 1976.