Sea Urchin Facts, Sea urchin characteristics

Sea Urchin

There are about 950 living species of spiny marine animals called sea urchins. These animal species possess a spherical body with organs’ radial arrangement, shown by almost five pores’ bands running from mouth to anus over the internal skeleton. The sea urchins possess pentaradial symmetry whose skeleton is made of calcite. There is an ovoid-shaped body with spines; the underside is flattened, and the upper surface is domed.

In addition to it, the complex structure of the mouth is made up of five plates of calcium carbonate. They come in a wide range of colors, including red, blue, green, brown, and purple. The body size of the red sea urchin is about 18 centimeters or 7 inches. The average weight is about 454 grams or one pound though it depends on gonad development. There are many exciting and interesting facts about these animal species, some of which are as mentioned below;

Sea urchin food

The sea urchins also require a proper diet to meet their survival needs like other animals. They will eat anything floating by. The sharp teeth of sea urchins can grind up periwinkles, mussels, barnacles, kelp, plankton and scrape algae off rocks. These animal species are sought out as food by foxes, cod, sea stars, lobsters, and birds. There are almost 950 sea urchin species that are all edible.

As the lobes of purple and red species are large and visually more delicious, they have the highest demand globally. About 90% of wild sea urchins are harvested by drags or diving. The sea urchin food is not overly salty and is a little briny. The sea urchin food is called Uni which is creamy in texture. The fresh ones leave a sweet ocean flavor with zinc and iron taste on the tongue. 

Sea urchin characteristics

All 950 different sea urchin species live in the water of all temperatures, cold or warm. However, some species live among kelp forests, on coral reefs, and in shallows, while some find their homes in rocky sea beds. A hard outer shell is called a test made of calcium carbonate and no bony structure. The test is composed of small plate segments enclosing the entire sea urchin species. Their bodies possess a radial symmetry that can be further divided into five equal parts but may not be easy to be seen. The symmetry can however, be easily seen when looking at test or dried sea urchins. 

In addition to it, they have different ways of seeing various things. It is not easy to see looking at sea urchins how they see. They do not have prominent eyes in spikes but also respond to light. Scientists have recently developed a way of how sea urchins see. There are a number of genes associated with eyes that get activated in hundreds of tube-like feet they possess amongst the spines.

They not only use their feet to move but also use them to see various things. These animal species come in various colors, such as black, green, brown, and red, but the favorite one is purple. Furthermore, these fish use an armor suit to get protected from various predators, including the wolf eel, the starfish, the tigerfish, the sea otter, and human beings. 

Sea urchin egg

These animal species reproduce in the warmer seasons. Their mating season is in the spring. The female sea urchin lay eggs coated in jelly, keeping them close via their spines to get a hold of them. The eggs get fertilized externally. A swimming embryo forms within half a day and swims free until it is juvenile and gets sunk to the sea’s bottom. The baby sea urchins reach adulthood within approximately five years. These animals can live a full life of about thirty years. 

Sea urchin fossil

The sea urchins possess a hard shell called a test covered with tubercles or small knobs to which spines get attached to living echinoids. However, the spines and test parts are normally present in fossils. The echinoid tests possess a variety of shapes; they can either be flattened or globular, heart-shaped or rounded. These echinoid fossils are considered the fossilized sea urchin remains, spiny marine invertebrates living on the sea bed.

Sea Urchin

In addition to it, human beings have shown interest in these fossils for millennia, have imbued them with magical powers, have considered them lucky, and linked them to their deities. For example, the sea urchin fossils Rasmus found in Denmark are not only beautiful but are the cretaceous sea relics that covered the modern-day Denmark area about sixty-five million years ago. 

Sea urchin adaptations

The sea urchins possess various adaptations. For example, they are adapted to rocky tidepools by evolving five rigid, sharp teeth to scrape algae plants off the rocks. These animal species also use their hard teeth, grinding away the rocks and burrow a home in various rocks. Like many other animals living on the earth’s surface, the sea urchin species possess sharp claws to defend themselves against other animal species in their environments. These claws are close to their spine and located on their bodies.

If we talk about the purple sea urchin adaptations, they possess large spines that can get as long as about ½ of the total width of their bodies, which makes some of the individuals three to four inches across. These spines are also considered effective against those predators that might view these cushion-like animals as one of the unattractive food items. 

The unique fact about these animal species is their globe-like bodies are covered with a larger number of spines. The bony plates from the shell provide protection for the inner parts of sea urchins. Their radial symmetry shows that they can be divided into five equal parts. Furthermore, there is a muscular foot in the sea urchin that help them cling strongly to the rocks, preventing them from being washed out to the sea. Their bodies get prevented from being damaged by currents, debris, and rough waves through the hard shells. 

Sea urchin anatomy

The sea urchins are the flattened or spherical free-moving echinoderms with the covering of spines. Their soft tissue anatomy is easily characterized by the tube or ambulacral feet, highly specialized water muscular system with external appendages, a dominant digestive tract, and a varying number of gonads. Their skeleton or endoskeleton is enclosed by the epidermis. The plates fit tightly in some of the sea urchins. 


Sometimes people get confused and raise questions about the sea urchin species to clear their minds. Therefore, the answers to some of those raised questions are as mentioned below;

Can you eat a sea urchin?

The Japanese have given sea urchin food a specific name Uni. The sea urchin food can be consumed in various presentations, such as a flavorful addition to various pasta dishes and as a part of a sushi meal. There are no better ways to enjoy the slimy texture and buttery flavor of sea urchins. 

Are sea urchins poisonous to humans?

Research has shown that sea urchin bites are not considered poisonous to human beings. The sea urchins have venom but are not harmful when they bite or sting humans. Their venom will only trigger some allergic reactions or leave puncture wounds when humans are bitten by their pedicellaria or stung by their spines. However, they are not considered dangerous or harmful to human beings. 

Is eating a sea urchin healthy?

The sea urchin is considered rich in dietary fiber, beta carotene, and minerals that these species get from their kelp diet. These species are also high in Vitamin A and C which are usually present in winter squash and dark leafy greens. The sea urchin is high in omega-3 fatty acids like many fatty fish i.e., salmon. 

Why is Uni so expensive?

The Uni is considered expensive due to many reasons, such as lower state funding, growing demand, rising financial aid, the exploding cost of bloated student amenities packages, and administrators. The sea urchin food Uni is not overly salty and is a little briny. 


Various plants and animals are present throughout the world, having unique identification characters discriminating against them. The same is the case with the sea urchin species. Although there are many characters discriminating against these animal species, people are still confused about them.

There is no need to worry as this blog post has provided exciting facts and information about sea urchins. The sea urchins are the spherical echinoderms with flattened, oval-shaped bodies, possessing radial symmetry. It means their body can be decided into two equal parts.

There are many advantages to human beings as the sea urchin species are very healthy. For example, the sea urchin food called Uni is rich in beta-carotene, minerals, proteins, and vitamins A and C. People love eating sea urchin food. In addition to it, Uni leaves ocean flavor with unique zinc and iron taste on the tongue. It would help greatly if you read this article with great care and pay full attention. 

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