Is a Sea Urchin (Uni) a Shellfish? [Explained]

Yes, sea urchins or uni (edible parts of sea urchins) are considered shellfish. These fascinating creatures belong to the echinoderm class, making them invertebrates. People all over the world love eating shellfish, even though they are not crustaceans.

Sea urchins belong to the Echinoidea class of echinoderms. People know them for their round and spiky shape.

These interesting sea creatures have hard, round shells called tests. The shells are 3 to 10 centimeters wide and have protective spines.

In this article, you’ll learn about sea urchins and why they’re called shellfish. Let’s embark on a quest for the unknown.

What Is a Shellfish?

Shellfish are sea creatures with hard outer shells that people eat, such as clams, crabs, and sea stars. Despite their common name, shellfish are not classified as fish. Interestingly, some shellfish thrive in freshwater, while most are harvested from saltwater.

It is interesting to know that farming shellfish helps the environment. It makes reefs grow, cleans water, and uses up waste. In certain areas, shrimp farming can harm the environment due to unsustainable harvesting methods.

sea urchin

Shellfish are nutrient-rich and can be a healthy addition to your diet. However, be mindful of allergies and dietary considerations. Consult a healthcare expert for personalized guidance.

According to FSR Magazine, here are some tips for selecting the freshest shellfish:

  • 1.    Purchase fresh shellfish from a store or reliable fishmonger.
  • 2.    In the U.S., check the FDA’s “maximum shelf life” or “use-by-date” on shellfish packaging.
  • 3.    Examine shellfish labels for information on when and where they were harvested.
  • 4.    Choose shellfish with a clean, seaside aroma.
  • 5.    Ensure they are clean and free from mud or grime. Avoid those that feel filmy or slimy.

In short, shellfish are not fish. However, people worldwide enjoy them because they are nutritious seafood. (Source)

Why Is a Sea Urchin (Uni) a Shellfish?

Uni or sea urchins are seen as shellfish because they are related to other echinoderms like sea cucumbers and sea stars. Shellfish and fish are different, but both are classified as seafood.

According to “The World Link” sources, “Sea urchins are gathered commercially at a high rate, just below Dungeness crab and pink shrimp. Their reproductive organs, called “uni,” are in high demand for their delicious taste and variety of colors.” (Source)

This association of sea urchins with shellfish in culinary contexts dates back to ancient times. Sea urchins are shellfish because their anatomy resembles that of a sea animal, like other shellfish. Over time, as our understanding of these animals evolved, so did their classification.

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What Is a Sea Urchin Classified As?

Sea urchins are classified as phylum Echinodermata. These are related to starfish, sea cucumbers, sea stars, and octopuses.

These animals live in different parts of the ocean, but they are mostly found near the coast and intertidal zone.

Sea urchins are usually rather small, around 1 foot (0.3 m) and have rounded bodies. Most sea urchins are predators and feed on other invertebrates, particularly those from the ‘phylum zoa.’

Class Echinoidea are commonly called sea urchins but are not closely related to true urchins.

Is Sea Urchin (Uni) Seafood?

Yes, it’s true. Uni (refers to the edible part of a sea urchin) or Sea urchins are seafood. However, many countries and regions do not consider sea urchins a delicacy.

If you plan to consume sea urchins raw, you should be aware that their taste may not be at its best. This can affect your dining experience and your palate’s satisfaction. However, it completely depends on your food culture and habit.

If they are dead, they are still a good source of protein. When sea urchins are cooked, they may have a slightly sweet flavor, similar to many other kinds of seafood.

If you wonder about sea urchins availability, you will be surprised to learn that pet stores and farm markets commonly sell sea urchins. When you encounter them at the store, they are typically in their fresh state.

Are Sea Urchins Crustaceans or Mollusks?

No, sea urchins cannot be counted in the category of crustaceans or mollusks. Sea Urchin belongs to the echinoderms, one of three shellfish classes.

sea urchin

The Crustacean family of shellfish includes crabs, lobsters, shrimps, barnacles, decapods, amphipods, remipedes, isopods, and copepods. The class of the crustacean family is Mandibulata.

What Seafood Can You Eat If You Have a Shellfish Allergy?

If you have shellfish allergy, you can safely enjoy mollusks. Mollusks like squid, oysters, scallops, and snails are seafood. They are safe for people with shellfish allergies.

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But make sure to ask your server about fish instead of shellfish due to cross-contamination risks.

Be aware of the potential symptoms of a shellfish allergy, which may include:

  • Hives
  • Itchy, irritated skin
  • Nasal stuffiness (congestion)
  • Swelling of the lips, face, tongue, throat, or other parts of the body
  • Wheezing or trouble breathing
  • Coughing, choking, or a tight feeling in the throat
  • Abdominal pain, diarrhea, nausea, or vomiting
  • Dizziness, lightheadedness, or fainting

Let’s see what the Mayo Clinic says about it,

“An allergy to shellfish is one of the most prevalent food allergies. People who are allergic to shellfish may have a reaction to all shellfish or a specific species. There is a wide spectrum of reactions, from relatively harmless ones like hives or a runny nose to severe ones that can be fatal.” (Source)

If you are allergic to shellfish, it is very important to stay away from the kinds of shellfish that you are allergic to. Crustaceans are the most common type of shellfish that cause allergies.

If you have trouble with shellfish, you might still be able to eat fish. However, it’s important to talk to a doctor about which foods are safe for you.

Is Sea Urchin Poisonous?

Yes, sea urchins can indeed be poisonous, but the good news is that sea urchin stings are typically not fatal. However, they can be very painful and may cause infections. This can result in symptoms such as swelling, redness, and warmth in the affected area.

It’s important to note that sea urchin allergies are rare. If you have a mild reaction, it’s a good idea to see a healthcare professional for evaluation.

Let’s see what Medical News Today’s researchers have investigated about poisonous sea urchins:

“Some people are also allergic to sea urchins, and their reactions can range from moderate to life-threatening. Those who have already experienced severe reactions to insect bites or stings may be at a higher risk.”

They further added,

“Their stings are notorious for being excruciatingly painful and sometimes even breaking skin, tissue, or bone.”

Sea urchin stings hurt a lot and can harm the skin, tissues, or even bones.

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So, be careful when you come across these dangerous sea creatures. Avoid touching or disturbing them and be particularly careful not to step on them.

What Is the Black Stuff Inside Sea Urchins?

Inside sea urchins, there is a black staff that has partially digested food. This food can be seaweed or other organic matter. It’s not typical food, and as such, it could be potentially poisonous. Therefore, it’s advisable to wash your hands after handling it.

It’s important to mention that some people may have strong reactions to this substance. This can cause paralysis. If you have skin problems, a high fever, or diarrhea, this substance might be causing your symptoms.

Frequently Asked Questions (FAQs)

1. Can you be allergic to sea urchins?

Yes, it’s a fact that you can be allergic to sea urchins. However, it can be mostly mild allergic reactions to sea urchins and usually is not deadly.

You should avoid touching and eating sea urchins to live a healthy lifestyle.

2. What seafood is not shellfish?

Fish are not shellfish, and they are the best seafood to eat if you are allergic to shellfish seafood.

Fish may include:

  • Anchovy
  • Bass
  • Bluefish
  • Carp
  • Catfish
  • Char
  • Cod
  • Flounder
  • Haddock
  • Halibut
  • Herring
  • Orange roughy
  • Mahi-mahi
  • Sardines
  • Salmon
  • Trout, and
  • Tuna.

However, it must be noted that many kinds of seafood containing fish items may also cause allergies just as shellfish.

3. Is Sea Urchin meat?

Sea urchins have a small amount of meat known as gonads or corals (Uni in the Japanese language). It smells strongly of the sea and tastes rich and buttery. Sea urchin is an acquired taste due to its richness and distinctive flavor.


Many people are concerned about being allergic to sea urchins, as they are very common shellfish.

However, sea urchins are widely known for food dishes. They are one of the most demanding types of shellfish known as echinoderms.

I hope this info helps you understand the connection between sea urchins and shellfish.

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