What are the Smallest Animals in the Ocean?

You may have found yourself at some point wondering what the smallest animal on earth is, perhaps during a conversation. The short answer is that it’s probably a creature that lives in the ocean! We’re going to show you why with this list of tiny animals. 

You may be surprised to hear that sometimes, being a small fish in a big ocean can have a lot of advantages. The ocean is home to so many cool small sea creatures and contains a lot of little fish, but these tiny sea creatures can be a little tricky to find. You can’t even measure them in inches! If you’re less than 4 mm small, the world can seam a whole lot bigger.

What is the Smallest Animal In the Ocean?


You may already know that the ocean is home to the biggest animal in the world, the Blue Whale. What you may not know is that it’s also home to potentially the smallest animal in the world. A lot of scuba divers don’t even notice a lot of these tiny sea creatures when they are diving.

What do you call the smallest creatures in the ocean? A lot of the small ocean animals that reside in the oceans around the world are actually bacteria and viruses, so they can be all but invisible to the naked eye. If you put them under the microscope though, you’ll see some pretty adorable tiny sea creatures! 

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While these may be the smallest animals in the world, you should not be fooled. These microscopic sea animals are equally as important to the ocean and its ecosystems. Any scientist that studies these creatures will tell you the same thing.

In no specific order, we’ve compiled below a list of the top 10 smallest creatures from the ocean. This can range from marine viruses and the smallest organisms in the ocean up to the impressively awesome Irukangji Jellyfish.

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1. Marine Viruses

Marine Viruses

We’re starting small here - microscopically small! Marine viruses live much like they do on land, and some of them are even as small as 40 nanometers (nm). You hear that correctly, not even mm or inches. You may be wondering, what exactly is a nanometre? 

Today, you may associate the word nano with a sim card that you would use for a smartphone, for instance, in order to give this a little bit of perspective. A nanometre is one billionth of a meter - so yes, it’s pretty small to say the least! In fact, it’s the smallest known.

The largest marine viruses are able to grow up to 400 nm in diameter and are still invisible to the naked eye. You’ll need a pretty strong microscope to see them. Marine viruses are able to come in a range of different sizes and can have some destructive capabilities. There are millions of these tiny things right out there in the deep blue! 

Marine viruses were discovered through epifluorescence and electron microscopy of ecological water samples by scientists. This followed the metagenomics sampling of uncultured viral samples. Pretty neat, or at least we think so! 

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2. Marine Bacteria

Marine Bacteria

Much like marine viruses, marine bacteria exist much like they do on the surface, and the ocean has infinite marine bacteria living inside of it. Marine bacteria are actually the second smallest organisms that you will find in the sea!

While they are larger than marine viruses, a lot of marine bacteria are still incredibly small in size. In fact, some only measure 1000 nm in length. This may seem a little bit larger than marine viruses but you still won’t see them without a pretty impressive microscope. 

Marine bacteria that live in the ocean is becoming an increasingly more popular field within marine biology. Actually, did you know that in only one milliliter of seawater you will be able to find up to a million microscopic organisms that are alive and existing? They are small but most certainly mighty, as they play a huge role in the ocean environment. Who knew bacteria could be so handy? 

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3. Algae

sea Algae

The sea house some of the world’s smallest plant organisms. A lot of there are single celled green algae specimens. These are roughly five times larger than the marine bacteria, and can measure from 5000 nm (5 micrometers). Sadly being so teeny tiny can leave these algae to become prey to slightly larger, while still also tiny, ocean creatures. As far as size is concerned algae can widely vary, and can range from the smallest known microscopic mircomonas species to the gigantic kelps, and these can be known to grow up to 60 meters (200 feet) tall.

In addition to the ecological role they play both by producing oxygen and by providing food for a lot of ocean life, algae are a source of crude oil and as such can be used in some foods, and even pharmaceutical and industrial products that are used by people.

Kelp is becoming increasingly popular because it’s so delicious and the oil it makes is so useful, so giant kelp forests have now been given an endangered status. 

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4. Dwarf Lantern Shark

Dwarf Lantern Shark

So, what exactly is the tiniest sea creature in the vast ocean? You’ll never guess - it’s a shark and it’s actually made its way into out list of the top 10 smallest animals found in the ocean. The dwarf lantern shark is the smallest shark, and possibly the smallest fish in the ocean. It’s actually likely the smallest animal in the world of sharks, and it’s super cute too!

The largest dwarf lantern shark that has ever been found measures only 7.8 inches (20 cm) in body length. These tiny sea creatures are found in the upper continental slopes off from Venezuela and Colombia. They live at a depth of around 283 to 439 meters (928 - 1440 ft)

You can recognize the lantern shark not only by looking at its small size even when it’s fully grown, but you can also identify it by its long flattened head, and it also has a mid-dorsal line and black ventral markings.

These really cool sea creatures are even able to create light from their array of photophores, and while the dwarf lantern shark generally doesn’t get targeted by commercial fishing companies, the species may end up becoming threatened because of ‘by-catch’, similar to many other endangered shark species. It is currently unknown what impact this creature has on human activity. 

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5. Sexy Shrimp

Sexy Shrimp

Hold up - What? There’s an actually shrimp that goes by this name? Sure, you may not think that the sexy shrimp matches with your particular kind of sexy, but there is a reason that the Thor Amboinensis species is also referred to as the sexy shrimp. It’s because of its strange body movements. 

This interesting nickname is actually derived from the way that they move their abdomen back and forth with quite an exotic flair. These little guys can grow up to 1-¼ inches in body length but generally they are much smaller than that, certainly one of the smallest marine creatures.

They are most often found in the reefs of the Indo-Pacific, and usually you can find them hidden among the anemone tentacles. These cool little dudes are a popular photograph subject among macro photographers. Also, while these are very small marine creatures they certainly make up for this in color. They have a very vibrant orange colored body that is adorned with white polka dots. They are most definitely one of the most adorable small water animals in the ocean, we think! 

6. Juvenile Frogfish

Juvenile Frogfish

A lot of divers really like looking for frogfish when they are underwater, and they particularly grab the attention of underwater photographers. They are very popular, but they can be a little hard to find because they are well camouflaged and can adapt to their surroundings easily. 

These marine creatures can be found in a bunch of sizes and colors, but these miniscule saltwater fish are genuinely incredibly ugly. They are so ugly that they are almost cute, but maybe we’re biased because we think all of these creatures are adorable!

An adult frogfish can frow from an inch up to 22 inches, but of course on this list we are talking about the baby frogfish.

Some frogfish can actually be even smaller than in inch long in size, or can only grow up to a few milimeters in some cases, though this does depend on the type. Their small size means that they are hard to find, but finding them will definitely be worth the effort! 

7. Nudibranch


For a lot of people that don’t go diving, the notion of a sea dweller that’s a little like a slug may be uninteresting or even boring - those people would be sorely mistaken. For divers, the opinion on these sea creatures is a little different. Nudibrachs are tiny little snippets of the ocean that are highly sought out by scuba divers.

This is a miniscule species full of color, and it can grow up to 12 inches (30cm) long. Some of the smallest versions of these creatures can be less than ¼ inch long (4mm) and that’s why they are on our list for being yet another small sea animal. It’s also very well known for its colors.

This sea critter has a range of breathtaking colors and extraordinary forms, but the creature actually seems a little helpless on first glance. To the contrary, these creatures are not helpless. Over 3000 different species of nudibranchs have been discovered up to the time of this article being written, and more and more of them are being found and studied on a daily basis.

8. Pygmy Seahorse

Pygmy Seahorse

This is yet another fan favorite that is well loved by scuba divers. The pygmy seahorse is a beautiful tiny saltwater fish that spends its entire life residing on soft corals and sea fans. They are generally found in warm tropical waters.

The seahorses can grow up to the average size of a human fingernail so they’re very small - they usually don’t grow much larger than an inch (2.4 cm) long. Juvenile pygmy seahorses are usually so small (measuring only a couple of millimeters) that they are almost invisible to the eye of the diver. They are also very well camouflaged in their surroundings too, making them even harder to find. 

These aren’t only the smallest type of seahorses in the sea, but they’re also a very popular creature among photographers. Because these animals are so small, they are very hard to see. If you are able to find them and get a picture though, you should take note that these little marine marvels don’t actually have eyelids so they can be quite sensitive to light. 

9. Octopus Wolfi

Octopus Wolfi

This is actually the world’s smallest known octopus! It’s a pretty cute marine creature too. You can find these miniscule creatures in the shallow waters of the western Pacific Ocean, and they are a real sight to behold for divers and ocean photographers.

These octopus are characterized by the pattern that is formed by papillate fringes around the edges of its suckers. The reason it is on our list is because it measures around 2.5 cm (1 inch) in length and it tends to weigh less than 1g (0.04 oz). If you think this octopus is cool, you should definitely have a look at our gift ideas for octopus lovers here! 

10. Irukandji Jellyfish

Irukandji Jellyfish

You may remember Dory’s friend Squishy from Finding Nemo. This is essentially the real life version of ‘squishy’ but don’t get too close and touch it because you may get stung!

In fact, the Irukandji Jellyfish is cute but so, so deadly. This is actually a kind of venomous box jellyfish. They can grow to an adult size measuring only around 1cm long, and they aren’t only one of the smallest jellyfish in the oceans that we currently know of, but they are also one of the most venomous. Unsurprisingly, like most of the venomous animals in the world, they can be found in Australia. 

These jellies are able to fire their stingers right into their victim. Unlike a lot of other jellyfish too, their stingers can be found in their bells in addition to their tentacles. You don’t want to cross this little guy, because he sure will bite back! 

Frequently Asked Questions

So here it is - our list of the world’s smallest ocean creatures. In order to give you even more information that you can use at your next pub quiz, we’ve also gone out of our way to answer some of the most frequently asked questions about the smalled creatures found in the universe. 

What is the smallest animal on earth at the moment?

This title most likely goes to the Brookesia Micra chameleon. These only grow to around 1 inch, and these chameleons are from Madagascar. They are so small that they were only discovered back in early 2012!

Closely following this is actually the world’s smallest mammal and this is Kitti’s Hog-nosed bat which measures on average around 1.1 inches.

What is the smallest living thing in the world? 

If you want to find the smallest thing alive in the universe then you’re going to need an impressive microscope. The smallest living thing would be a virus, organism or bacteria. The smallest known though would be between the Irukandji jellyfish and a small parasitic jellyfish known as Myxozoa. 

What are the biggest and smallest animals in the world?

There is such a massive difference between the biggest and smallest animals in the world. The smallest is wildly debated, so let’s say they are both mammals. The biggest would be the blue whale and the smallest would be Kitti’s hog nosed bat. 

There is certainly no doubt that the Blue Whale is the largest, but for the smallest we should also mention the Irukandji jellyfish and a parasitic jellyfish that’s called Myxozoa. 

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