The Giant Siphonophore and More of the Largest Living Sea Creatures

The ocean contains some of the largest creatures on Earth. Here you can meet some of the largest living sea creatures. Some have fierce reputations while others are enormous, gentle giants. 

Each marine phylum has its own largest creatures, but this slide show contains some of the largest creatures overall, based on maximum recorded measurements of each species.

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Blue Whale

Blue Whale
Blue Whale. Fotosearch/Getty Images

The blue whale is not only the largest creature in the ocean, but it's also the largest creature on Earth. The largest blue whale ever measured was 110 feet long. Their average length is about 70 to 90 feet. 

Just to give you a better perspective, a large blue whale is about the same length as a Boeing 737 airplane, and its tongue alone weighs about 4 tons (about 8,000 pounds, or about the weight of an African elephant).

Blue whales live throughout the world's oceans. During warmer months, they are generally found in cooler waters, where their main activity is feeding. During cooler months, they migrate to warmer waters to mate and give birth. If you live in the U.S., one of the most common whale watching destinations for blue whales is off the coast of California. 

Blue whales are listed as endangered on the IUCN Red List, and are protected by the Endangered Species Act in the U.S. The IUCN Red List estimates the worldwide blue whale population at 10,000 to 25,000. 

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Fin Whale

Fin Whale
Fin Whale. anzeletti/Getty Images

The second-largest sea creature -- and second-largest creature on Earth -- is the fin whale. Fin whales are a very slender, graceful whale species. Fin whales can reach lengths up to 88 feet and weigh up to 80 tons.

These animals have been nicknamed "the greyhounds of the sea" because of their fast swimming speed, which is up to 23 mph. 

Although these animals are very large, their movements are not well understood. Fin whales live throughout the world's oceans and are thought to live in cold waters during the summer feeding season and warmer, subtropical waters during the winter breeding season.

In the United States, places you could go to see fin whales include New England and California.

Fin whales are listed as endangered on the IUCN Red List. The worldwide fin whale population is estimated at around 120,000 animals.

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Whale Shark

Whale Shark
Whale Shark and Divers. Michele Westmorland/Getty Images

The trophy for world's biggest fish isn't exactly a "trophy fish"... but it's a big one. It's the whale shark. The whale shark's name comes from its size, rather than any characteristics resembling a whale. These fish max out at about 65 feet and can weigh up to 75,000 pounds, making their size rival some of the largest whales on Earth. 

Similar to large whales, though, whale sharks eat small creatures. They filter-feed, by gulping in water, plankton, small fish and crustaceans and forcing the water through their gills, where their prey gets trapped. During this process, they can filter over 1,500 gallons of water in an hour. 

Whale sharks live in warmer temperate and tropical waters around the world. One place to see whale sharks close to the U.S. is Mexico.

The whale shark is listed as vulnerable on the IUCN Red List. Threats include overharvesting, coastal development, habitat loss and disturbance by boaters or divers.

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Lion's Mane Jelly

Lion's Mane Jellyfish
Lion's Mane Jellyfish. James R.D. Scott/Getty Images

If you include its tentacles, the lion's mane jelly is one of the longest creatures on Earth. These jellies have eight groups of tentacles, with 70 to 150 in each group. Their tentacles are estimated to be able to grow to 120 feet in length. This is not a web you'd want to get tangled in! While some jellies are harmless to humans, the lion's mane jelly can inflict a painful sting.

Lion's mane jellies are found in cooler waters of the North Atlantic and Pacific Oceans.

Perhaps to the chagrin of swimmers, lion's mane jellies have a healthy population size and haven't been evaluated due to any conservation concerns.

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Giant Manta Ray

Giant Manta Ray
A Pacific Giant Manta Ray. Erick Higuera, Baja, Mexico/Getty Images

Giant manta rays are the world's largest ray species. With their large pectoral fins, they can reach a span of up to 30 feet across, but average-sized manta rays are about 22 feet across. 

Giant manta rays feed on zooplankton, and sometimes swim in slow, graceful loops as they consume their prey. The prominent cephalic lobes extending from their head help funnel water and plankton into their mouth. 

These animals live in waters between the latitudes of 35 degrees North and 35 degrees South. In the U.S., they are primarily found in the Atlantic Ocean from South Carolina on the south, but have been spotted as far north as New Jersey. They may also be seen in the Pacific Ocean off Southern California and Hawaii. 

Giant manta rays are listed as vulnerable on the IUCN Red List. Threats include harvesting for their meat, skin, liver and gill rakers, entanglement in fishing gear, pollution, habitat degradation, collisions with ships, and climate change.

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Portuguese Man o' War

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

The Portuguese man o' war is another animal that is very large based on the size of its tentacles. These animals can be identified by their purplish-blue float, which is only about 6 inches across. But they have long, slender tentacles that can be more than 50 feet long. 

Portuguese man o' wars feed using their tentacles. They have tentacles used to capture the prey, and then stinging tentacles that paralyze the prey. Although it resembles a jellyfish, the Portuguese man o' war is actually a siphonophore.

Although they are occasionally pushed by currents into cooler regions, these creatures prefer warm tropical and subtropical waters. In the U.S., they are found in both the Atlantic and Pacific Oceans off the southeastern portions of the U.S. and in the Gulf of Mexico. They do not experience any population threats.

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Giant Siphonophore

Giant Siphonophore
Giant Siphonophore. David Fleetham/Visuals Unlimited, Inc./ Getty Images

Giant siphonophores (Praya dubia) can be even longer than a blue whale. Granted, these aren't really a single organism, but they bear mentioning in a list of the ocean's largest creatures.

These fragile, gelatinous animals are cnidarians, which means they are related to corals, sea anemones and jellyfish. Like corals, siphonophores are colonial organisms, so rather than one whole being (like a blue whale), they are formed by many bodies called zooids. These organisms are specialized for certain functions like feeding, movement, and reproduction -- and all strung together on a stem called a stolon so together, they act like one organism.

The Portuguese man o' war is a siphonophore that lives at the ocean surface, but many siphonophores, like the giant siphonophore are pelagic, spending their time floating in the open ocean. These animals can be bioluminescent.

Giant siphonophores measuring more than 130 feet have been found. They are found throughout the world's oceans. In the United States, they are found in the Atlantic Ocean, Gulf of Mexico and the Pacific Ocean.

The giant siphonophore has not been evaluated for conservation status.

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Giant Squid

Giant Squid
NOAA scientists with giant squid aboard the NOAA research vessel Gordon Gunter. The squid was caught in July 2009 while conducting research off the Louisiana coast in the Gulf of Mexico. NOAA

Giant squid (Architeuthis dux) are animals of legend -- have you ever seen an image of a giant squid wrestling with a ship or a sperm whale? Despite their prevalence in ocean images and lore, these animals prefer the deep sea and are rarely seen in the wild. In fact, most of what we know about giant squid comes from dead specimens found by fishermen, and it wasn't until 2006 that a live giant squid was filmed.

Measurements of the largest giant squid vary. Measuring these creatures can be complicated since tentacles may be stretched or even lost. The largest squid measurements vary from 43 feet to over 60 feet, and the largest is thought to weigh about a ton. The giant squid is estimated to have an average length of 33 feet. 

In addition to being one of the largest animals in the world, giant squid also has the largest eyes of any animal -- their eyes alone are about the size of a dinner plate.

Not much is known about the giant squid's habitat because they are rarely observed in the wild. But they are thought to frequent most of the world's oceans and tend to be found in temperate or subtropical waters. 

The population size of the giant squid is unknown, but researchers determined in 2013 that all giant squid that they sampled had very similar DNA, which led them to presume that there is one species of giant squid rather than different species in different locations.

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Colossal Squid

Colossal squid (Mesonychoteuthis hamiltoni) rival the giant squid in size. They are thought to grow to lengths of about 45 feet. Like the giant squid, the habits, distribution and population size of colossal squid are not well known, as they are not often observed alive in the wild. 

This species wasn't discovered until 1925 -- and only then because two of its tentacles were found in a sperm whale's stomach. Fishermen caught a specimen in 2003 and hauled it aboard. To give a better perspective on size, it was estimated that calamari from the 20-foot specimen would have been the size of tractor tires. 

Colossal squid are thought to live in deep, cold waters off New Zealand, Antarctica, and Africa.

The population size of colossal squid is unknown.

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Great White Shark

White Shark
White Shark. Image Source/Getty Images

A list of the largest creatures in the ocean wouldn't be complete without the ocean's largest apex predator -- the white shark, commonly called the great white shark (Carcharodon carcharias). There are conflicting reports as to the largest white shark, but it is thought to be about 20 feet. While white sharks in the 20-foot range have been measured, lengths of 10 to 15 feet are more common.

White sharks are found throughout the world's oceans in mostly temperate waters in the pelagic zone. Places white sharks can be seen in the United States include off California and the East Coast (where they spend the winters south of the Carolinas and the summers in more northerly locales). The white shark is listed as vulnerable on the IUCN Red List.

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Kennedy, Jennifer. "The Giant Siphonophore and More of the Largest Living Sea Creatures." ThoughtCo, Sep. 3, 2021, Kennedy, Jennifer. (2021, September 3). The Giant Siphonophore and More of the Largest Living Sea Creatures. Retrieved from Kennedy, Jennifer. "The Giant Siphonophore and More of the Largest Living Sea Creatures." ThoughtCo. (accessed March 25, 2023).