Jellyfish vs. Man O’ War: What Are 8 Key Differences?

Written by Jennifer Gaeng
Updated: October 2, 2023
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Although sometimes confused for one another, the jellyfish and the Portuguese man o’ war are two different ocean creatures. They have tentacles, they sting, and they should be avoided at all costs. To the untrained eye, they are nearly identical. It may not seem important to know what makes them unique, but knowledge is power, especially if you are planning a visit to the beach soon!

A Comparison 

JellyfishMan O’ War
SizeAverage Width – 3 ft; Tentacles Up to 100 ftFloat – Up to 6 inches; Tentacles Up to 160 ft
ColorsVarious ColorsPurple-Blue, Pinkish
Physical Features3 Parts: Umbrella, Oral Arms, and Stinging Tentacles4 Parts: Bladder, Tentacles, Digestive System, Sex Organs
DangerVenomous; Pain Level Varies, Can Be Life-ThreateningVenomous; Incredibly Painful, Rarely Fatal
DietPassive Eater; Mainly Shrimp and Small FishPassive Eater; Small Fish, Plankton, Crustaceans, Worms
Lifespan1 – 3 Years, Some Species Much Longer1+ Years
HabitatsAll Across the Worlds OceansWarm Waters; Atlantic and Pacific Oceans
HabitsCan Rise, Dive, and Swim – Floats via Belly ContractionsFloats and Feeds, Incapable of Swimming, Uses Ocean Currents

Key Differences Between Jellyfish vs. Man O’ War

The key difference between a jellyfish and a Portuguese man o’ war is that the Portuguese man o’ war is a siphonophore, a group of specialized animals called zooids that act together as a unit. The jellyfish is a single animal. They also differ in size, appearance, physical features, lifespan, habits, habitats, and diet.

Although both are part of the phylum Cnidaria, the Portuguese man o’ war (Physalia physalis) is a species of siphonophore, which is a genus of creatures closely related to jellyfish. Jellyfish belong to the family Cyaneidae. Let’s explore some more key differences between these interesting sea creatures.


What do Jellyfish Eat and How Do They Do It?

Jellyfish can range from 1 mm to 16 inches.


In size, jellyfish can range from one millimeter to 16 inches. When fully grown, the lion’s mane jellyfish (Cyanea capillata) can measure up to three feet across. Rarely they can reach a width of over 6 feet (1.8 m) and a length of over 100 feet (30 m) with their tentacles! Portuguese man o’ war’s feeding tentacles can measure up to 160 feet (50 meters) in length, and their float can measure up to 6 inches (15 centimeters).


In terms of color, jellyfish can come in a wide range of hues from yellow to deep blue to vivid purple to pale lilac to bright orange to deep red. Luminescence is a term used to describe the icy, dazzling light that some jellyfish emit when disturbed at night. They are not able to change their color at will. Most of them will change color as they become older.

The blue, violet, or pink float of the man o’ war resembles a Portuguese naval ship under full sail from the 18th century, hence the name. A man o’ war’s bladder is a floaty blue, violet, or pink tint. Its color lets it blend in with the ocean’s water, surprising and stinging its prey.

Physical Features

moon jellyfish

Jellyfish lack bones, brains, and eyes.

©Vladimir Wrangel/

Having a smooth body with small tentacles, jellyfish can sting other organisms. They lack bones, brains, hearts, and eyes. These creatures’ mouths are in the center of their bodies. They are perfectly concealed by their body, which is 95% water! The umbrella, oral arms (around the mouth), and stinging tentacles are the three primary elements of a jellyfish’s body. They have an interior cavity for digestion.

The Portuguese man o’ war is a siphonophore, a group of specialized animals called zooids that act together. The uppermost polyp contains the gas-filled bladder; the second has the stinging tentacles covered in nematocysts; the third contains the muscle that moves food to the digestive system, and the fourth contains the reproductive organs. Individual colonies of man o’ war are made up of either all-female polyps or all-male polyps, depending on the species. Physalia utriculus, often known as bluebottles in the Pacific and Portuguese man o’ war in the Atlantic, is one of the most identifiable.


Jellyfish stings are rarely life-threatening. Pain, redness, itching, numbness, and tingling are all common after a jellyfish sting. Some jellyfish stings, such as those from the marine wasp-like box jellyfish, are exceedingly severe and even lethal. In recognition of its status as the deadliest jellyfish in the ocean, the box jellyfish is one of the most hazardous creatures on Earth. There are numerous species of jellyfish in the box jellyfish family. Approximately 50 kinds of box jellyfish exist, some more hazardous than others.

Fish and other small animals can be paralyzed and killed by their poisoned nematocysts. However, Man-of-war stings, although incredibly painful for humans, are rarely fatal. A dead man o’ war that washes ashore might still sting. The venom can cause extreme discomfort in humans, as well as skin welts or an allergic reaction. If you see a Portuguese man o’ war, keep your distance and observe it from afar! If stung, monitor your symptoms and seek medical attention. Systemic reactions are not uncommon, but they are rarely life-threatening.


With most jellyfish, feeding occurs in a “passive” fashion. This means that they float around the ocean, feeding on anything they can fit in their mouths, from tiny shrimp to small fish.  The coelenteron is the jellyfish’s stomach and intestines in one place. Internal body cells create digestive enzymes that break down food that reaches the jellyfish’s intestine. Using these cells, the jellyfish can absorb and distribute nutrients throughout its entire system.

The Portuguese man o’ war is a carnivore that eats small fish, plankton, worms, and crustaceans. Rather than going out in search of food, the colony catches prey as it moves across the surface of the ocean.


Portuguese Man O' War - Physalia physalis - at the surface of the Atlantic Ocean, Madeira.

Portuguese man o’ war has a lifespan of at least one year.


In general, the average life span of a Portuguese man o’ war is at least one year. The usual lifespan of a jellyfish is between one and three years. Some jellyfish species, on the other hand, can live for decades while others survive for only a few days.

Also, did you know that scientists have discovered some jellyfish may live endlessly? Known scientifically as Turritopsis dohrnii, the “immortal Jellyfish” can apparently live for a thousand years or more in the appropriate conditions. One reason for this is that, after reproduction, this jellyfish may revert to its “baby” stage (a juvenile polyp). Despite not being affected by aging, predators can nonetheless kill jellyfish.


The Portuguese man o’ war prefers the warmer waters of the tropics and subtropics. These colonies thrive in the warm waters of the Atlantic and Pacific oceans, including the Gulf Stream, the Indian Ocean, the Caribbean Sea, and the Sargasso Sea, where the water is warm enough for them.

Jellyfish can be found across the world’s oceans, from the depths of the deep sea to the wide waters of the open ocean and even the freezing waters of the Arctic. However, most jellyfish are found along coastlines. There are a variety of species that can be found in both fresh and saltwater environments.


In response to sensory stimulation, jellyfish rise to the surface, dive to avoid rock walls, form aggregations, and swim horizontally in response to turbulent waters. They move ahead by rhythmically expanding and contracting their bellies (but aren’t powerful enough to withstand the direction of most ocean currents).

Portuguese man o’ wars are vicious predators. Small fish, pelagic crustaceans, and other invertebrates are stung and paralyzed by their feeding tentacles. Flotation, prey acquisition, feeding, and reproduction are just a few of the tasks that each of a man o’ war’s four distinct components is responsible for. The Portuguese man o’ war is incapable of swimming. Instead, it is propelled forward by the force of wind and ocean currents.

Wrapping Up Jellyfish vs. Man O’ War

The Atlantic Portuguese man o' war (Physalia physalis), also known as the man-of-war, blue bottle, or floating terror, is a marine hydrozoan. Isolated on white background.

Portuguese man o’ war belongs to the siphonophores family of creatures.


The jellyfish and the man o’ war have a lot in common with one another. For example, their prey is easily stunned and captured by their stinging tentacles. Also, smaller species of fish and plankton are the primary sources of food for both species. Their similarities cease there, though. For example, jellyfish are classified as Medusozoan, while Portuguese man o’ war belongs to the Siphonophores family. The adults of the jellyfish species have a single gelatinous body; however, the man-of-war is made up of a cluster of four polyps that coexist.

The photo featured at the top of this post is © Igor Kovalchuk/

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About the Author

Jennifer Gaeng is a writer at A-Z-Animals focused on animals, lakes, and fishing. With over 15 years of collective experience in writing and researching, Jennifer has honed her skills in various niches, including nature, animals, family care, and self-care. Hailing from Missouri, Jennifer finds inspiration in spending quality time with her loved ones. Her creative spirit extends beyond her writing endeavors, as she finds joy in the art of drawing and immersing herself in the beauty of nature.

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