Identification of Jellyfish and Jelly-like Animals

Diver and Purple-Striped Jellyfish
Douglas King / Moment / Getty Images

While swimming or walking along the beach, you encounter a jelly-like animal. Is it a jellyfish? Can it sting you? Here is an identification guide to commonly-seen jellyfish and jellyfish-like animals. You can learn basic facts about each species, how to identify them, if they are true jellyfish, and if they can sting.

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Lion's Mane Jellyfish

A Lion's Mane Jelly in the White Sea
Alexander Semenov / Moment Open / Getty Images

The lion's mane jellyfish is the world's largest jellyfish species. The largest lion's mane jellyfish have a bell that is over 8 feet across, and tentacles that can stretch anywhere from 30–120 feet in length. 

Is it a Jellyfish? Yes

Identification: Lion's mane jellyfish have a pink, yellow, orange, or reddish brown bell, that gets darker as they age. Their tentacles are thin, and often found in a mass that looks like a lion's mane.

Where it is Found: Lion's mane jellyfish are a cool water species—they are most often found in waters less than 68 degrees Fahrenheit. They are found in both the northern Atlantic and Pacific Oceans.

Does it Sting? Yes. While they're sting isn't usually lethal, it can be painful. 

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Moon Jelly

Moon jelly (Aurelia aurita) aggregation, Caribbean, Atlantic Ocean
Mark Conlin / Oxford Scientific / Getty Images

The moon jelly or common jellyfish is a beautiful translucent species that has phosphorescent colors and graceful, slow movements. 

Is it a Jellyfish? Yes

Identification: In this species, there is a fringe of tentacles around the bell, four oral arms near the center of the bell, and 4 petal-shaped reproductive organs (gonads) which may be orange, red, or pink. This species has a bell that grows up to 15 inches in diameter.

Where it is Found: Moon jellies are found in tropical and temperate waters, usually in temperatures of 48–66 degrees. They may be found in shallow, coastal waters and in the open ocean.

Does it Sting? A moon jelly can sting, but the sting is not as severe as some other species. It may cause a minor rash and skin irritation.

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Purple Jellyfish or Mauve Stinger

Purple Jellyfish, Pelagia noctiluca
Franco Banfi / WaterFrame / Getty Images

The purple jellyfish, also known as the mauve stinger, is a beautiful jellyfish with long tentacles and oral arms.

Is it a Jellyfish? Yes

Identification: The purple jellyfish is a small jellyfish whose bell grows to about 2 inches across. They have a purplish translucent bell that is dotted with red and long oral arms that trail behind them.

Where it is Found: This species is found in the Atlantic, Pacific, and Indian Oceans.

Does it Sting? Yes, the sting can be painful and causes lesions and anaphylaxis (a severe allergic reaction).

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Portuguese Man-of-War

Portuguese Man o' War
Justin Hart Marine Life Photography and Art / Getty Images

The Portuguese man-of-war is often found washed up on beaches. They are also known as man o' war or blue bottles.

Is it a Jellyfish? Although it looks like a jellyfish and is in the same phylum (Cnidaria), the Portuguese man-of-war is a siphonophore in the class Hydrozoa. Siphonophores are colonial, and are made up of four different polyps—pneumatophores, which make up the gas float, gastrozooida, which are feeding tentacles, dactylozoodis, polyps that capture prey, and gonozooids, which are used for reproduction. 

Identification: This species can be easily identified by its blue, purple, or pink gas-filled float and long tentacles, which may stretch more than 50 feet.

Where it is Found: Portuguese man o' wars are a warm-water species. They may be found in tropical and subtropical waters in the Atlantic, Pacific, and Indian Oceans and the Caribbean and Sargasso Seas. Occasionally during stormy weather, they are washed into cooler areas.

Does it Sting? Yes. This species can deliver a very painful (but rarely deadly) sting, even if they are dead on the beach. Keep an eye out for their floats when swimming or walking along the beach in warm areas.

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By-the-Wind Sailor

By-The-Wind Sailor on Beach
Andy Nixon / Gallo Images / Getty Images

The by-the-wind sailor, also known as the purple sail, little sail, Vellela vellela, and Jack sail-by-the wind, can be identified by the stiff triangular sail on the animal's upper surface.

Is it a Jellyfish? No, it is a hydrozoan.

Identification: By-the-wind sailors have a stiff, triangular sail, blue float made up of concentric circles composed of gas-filled tubes, and short tentacles. They may up to about 3 inches across.

Where it is Found: By-the-wind sailors are found in subtropical waters in the Gulf of Mexico, Atlantic Ocean, Pacific Ocean, and Mediterranean Sea. They may wash ashore in large numbers.

Does it Sting? By-the-wind sailors can inflict a mild sting. The venom is most painful when it comes into contact with sensitive body areas, such as the eye. 

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Comb Jelly

Comb Jellyfish in the Adriatic Sea
Borut Furlan / WaterFrame / Getty Images

Comb jellies, also known as ctenophores or sea gooseberries, may be seen in the water or near or on shore in large masses. There are over 100 species of comb jellies.

Is it a Jellyfish? No. Although they are jelly-like in appearance, they are different enough from jellyfish to be classified in a separate phylum (Ctenophora).

Identification: These animals received the common name "comb jelly" from 8 rows of comb-like cilia. As these cilia move, they scatter light, which may produce a rainbow effect.

Where it is Found: Comb jellies are found in a variety of water types—polar, temperate, and tropical waters, and both inshore and offshore.

Does it Sting? No. Ctenophores have tentacles with colloblasts, which are used to capture prey. Jellyfish have nematocysts in their tentacles, which shoot out venom to immobilize prey. The colloblasts in a ctenophore's tentacles don't shoot out venom. Instead, they release a glue that sticks to the prey.

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A Salp Chain
Justin Hart Marine Life Photography and Art / Moment / Getty Images

You might find a clear, egg-like organism or mass of organisms in the water or on the beach. These are a jelly-like organism called salps, which are a member of the group of animals called the pelagic tunicates.

Is it a Jellyfish? No. Salps are in the phylum Chordata, which means they're more closely related to humans than jellyfish.

Identification: Salps are free-swimming, planktonic organisms that are barrel, spindle, or prism-shaped. They have a transparent outer covering called a test. Salps are found singly or in chains. Individual salps may be from 0.5–5 inches in length.

Where it is Found: Salps may be found in all oceans but are most common in tropical and subtropical waters.

Does it Sting? No

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Box Jellyfish

Box Jellyfish in Hawaii
Visuals Unlimited, Inc. / David Fleetham / Getty Images

Box jellies are cube-shaped when viewed from above. Their tentacles are located in each of the four corners of their bell. Unlike true jellyfish, box jellies can swim relatively quickly. They can also see fairly well using their four relatively complex eyes. You'll want to move out of the way if you see one of these, because they can inflict a painful sting. Because of their sting, box jellies are also known as sea wasps or marine stingers.

Is it a Jellyfish? Box jellyfish are not considered "true" jellyfish. They are classed in the group Cubozoa, and have differences in their life cycle and reproduction. 

Identification: In addition to their cube-shaped bell, box jellies are translucent and pale blue in color. They can have up to 15 tentacles that grow from each corner of their bell—tentacles that can stretch up to 10 feet. 

Where it is Found: Box jellies are found in tropical waters in the Pacific, Indian, and Atlantic Ocean, usually in shallow waters. They may be found in bays, estuaries, and near sandy beaches. 

Does it Sting? Box jellies can inflict a painful sting. The "sea wasp," Chironex fleckeri, found in Australian waters, is considered one of the most deadly animals on Earth. 

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Cannonball Jelly

A dead Cannonball Jellyfish on the beach, North Carolina
Joel Sartore / National Geographic / Getty Images

These jellyfish are also known as jellyballs or cabbage-head jellyfish. They are harvested in the southeastern U.S. and exported to Asia, where they are dried and eaten.

Is it a Jellyfish? Yes

Identification: Cannonball jellyfish have a very round bell that can be up to 10 inches across. The bell may have brownish coloration. Underneath the bell is a mass of oral arms that are used for locomotion and capturing prey.

Where it is Found: Cannonball jellies are found in the Gulf of Mexico and both the Atlantic and Pacific Oceans.

Does it Sting? Cannonball jellyfish have a minor sting. Their venom is most painful if it gets in the eye.

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Sea Nettle

Atlantic Sea Nettle (Chrysaora quinquecirrha)
DigiPub / Moment / Getty Images

Sea nettles are found in both the Atlantic and Pacific Ocean. These jellyfish have long, slender tentacles.

Is it a Jellyfish? Yes

Identification: Sea nettles may have a white, pink, purple, or yellowish bell that may have reddish-brown stripes. They have long, slender tentacles and frilly oral arms that extend from the center of the bell. The bell may be up to 30 inches in diameter (in the Pacific sea nettle, which is larger than the Atlantic species) and tentacles may extend as long as 16 feet.

Where it is Found: Sea nettles are found in temperate and tropical waters and may be found in shallow bays and estuaries.

Does it Sting? Yes, the sea nettle may impart a painful sting, which leads to skin swelling and a rash. Severe stings may result in coughing, muscle cramps, sneezing, sweating, and a feeling of constriction in the chest.

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Blue Button Jelly

Blue Button Jelly
Eco / UIG / Getty Images

The blue button jelly is a beautiful animal in the class Hydrozoa.

Is it a Jellyfish? No

Identification: Blue button jellies are small. They can grow to about 1 inch in diameter. In their center, they have a golden-brown, gas-filled float. This is surrounded by blue, purple, or yellow hydroids, which have stinging cells called nematocysts.

Where it is Found: Blue button jellies are a warm water species found in the Atlantic Ocean, Gulf of Mexico and Mediterranean Sea.

Does it Sting? While their sting isn't deadly, it can cause skin irritation.

References and Further Information

  • Cowles, D. 2004. Velella velella (Linnaeus, 1758). Walla Walla University. Accessed May 31, 2015.
  • Coulombe, D.A. The Seaside Naturalist. Simon & Schuster.
  • Invasive Species Compendium. Pelagia noctiluca (Mauve Stinger). Accessed May 31, 2015.
  • Iverson, E.S. and R.H. Skinner. Dangerous Sea Life of the Western Atlantic, Caribbean and Gulf of Mexico. Pineapple Press, Inc., Sarasota, FL.
  • Mills, C.E. Ctenophores. Accessed May 31, 2015.
  • National Geographic. Box Jellyfish. Accessed May 31, 2015.
  • Perseus. Jellyfish Spotting. Accessed May 31, 2015.
  • Smithsonian National Museum of Natural History. Jellyfish and Comb Jellies. Accessed May 31, 2015.
  • Souza, M. Cannonball Jellyfish. Accessed May 31, 2015.
  • van Couwelaar, M. Order Salipida. Zooplankton and Micronekton of the North Sea. Marine Species Identification Portal. Accessed May 31, 2015.
  • Waikiki Aquarium. Box Jelly. Accessed May 31, 2015.
  • Woods Hole Oceanographic Institution. 2010. The Salp: Nature's Near-Perfect Little Engine Just Got Better. Accessed May 31, 2015.
  • WoRMS (2015). Stomolophus meleagris Agassiz, 1862. Accessed through: World Register of Marine Species. May 31, 2015.
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Kennedy, Jennifer. "Identification of Jellyfish and Jelly-like Animals." ThoughtCo, Feb. 16, 2021, Kennedy, Jennifer. (2021, February 16). Identification of Jellyfish and Jelly-like Animals. Retrieved from Kennedy, Jennifer. "Identification of Jellyfish and Jelly-like Animals." ThoughtCo. (accessed March 23, 2023).