What to do in case of a sea urchin sting?

The area should be washed with soap and water, any accessible spines should be removed with sterilized tweezers, and a healthcare professional should be consulted if they are deep, there is inflammation, or signs of infection appear.

February 6, 2026

Sea urchin

Q: Is a sea urchin a fish or a crustacean?

Neither. It's an echinoderm, which means it's related to starfish and sea cucumbers.

Q: How do hedgehogs reproduce?

They reproduce sexually externally. They release their gametes (sperm and eggs) directly into the seawater, where fertilization occurs.

El sea urchin It is one of the most emblematic and ancient inhabitants of our oceans. Belonging to the phylum Echinodermata, this animal shares a direct relationship with starfish and sea cucumbers.

Common name: Sea urchin
Scientific name: paracentrotus lividus
Family: Parechinidae
Class: Echinoidea
Weight: Approximately between 50g and 200g
Diameter: Between 5 and 7 cm (not counting the spines)

Although at first glance it may seem like a static "ball of thorns", it is a complex organism with a fundamental role in the balance of marine ecosystems, especially on the Spanish coasts, from the Mediterranean to the Cantabrian Sea and the Atlantic.

In Spain, its presence is so common that it is part of the local culture, receiving regional names such as “sea urchins” in Asturias or “garotas” in Catalonia.

What is a sea urchin?

The sea urchin is an exclusively marine invertebrate animal that lives associated with the seabed, which in biology is known as an organism benthic. Not like others Marine animalsThey do not have a differentiated "head" or a centralized brain, but they do possess a nervous system capable of detecting light, chemicals, and predators.

If we analyze the sea urchin and its characteristics Main features, we find unique traits in the animal kingdom:

Pentaradial symmetry: Its body is organized into five equal parts around a central axis, similar to the segments of an orange.
Movable spikes: Their spines are not fixed; they are attached to the shell by a ball-and-socket system that allows them to move in all directions for defense and movement.
Longevity: They are hardy animals. For example, species like the lima or diadema hedgehog (Diadema africanum), common in the Canary Islands, have an estimated life expectancy of between 3 and 4 years, according to data from Canary Islands Government.
Assorted colors: Although dark, violet, greenish or reddish tones predominate in the Peninsula (such as the paracentrotus lividus), there are species with diverse colors.

Anatomy: The fascinating skeleton of the sea urchin

What makes the hedgehog a marvel of natural engineering is its internal structure. The animal's soft body is protected by a rigid, globular shell.

This sea urchin skeleton, also called “testa”, formed by fused plates of calcium carbonateThese plates form perfect geometric patterns and are perforated by tiny holes through which the animal extends its tube feet.

Inside this protective case lies one of the most complex organs in the marine world: the Aristotle's lantern.

What is Aristotle's Lantern? It's its chewing apparatus. It consists of a structure of five calcareous "teeth" or jaws that act like powerful pincers. Thanks to this mechanism, the sea urchin can scrape algae off rocks and even excavate shelters in the stone.
Ambulacral system: It's an internal hydraulic system. The hedgehog pumps water through channels in its body to inflate and deflate its "feet" (pods), allowing it to adhere to surfaces or walk slowly.

Habitat and distribution: Where do sea urchins live?

To respond to where sea urchins liveWe must look to the seabeds of the entire planet, although they prefer temperate and tropical waters. They are strictly marine animals.

Its depth distribution is extensive:

Intertidal zone: They are very common to find in tide pools that are exposed during low tide.
Rocky bottoms: They mainly inhabit rocky coastal areas. In species such as the diadema sea urchin, they can be found from intertidal pools to depths of about 30 or 40 meters.

On the coasts of SpainIts habitat varies slightly depending on the region:

Mediterranean: They usually hide in rock crevices or under stones to protect themselves from the waves.
Atlantic and Cantabrian: They are often seen associated with seagrass meadows or in rocky areas rich in marine vegetation.
Canary Islands: Here it is common to find large populations in rocky bottoms, sometimes forming areas of low vegetation known as "white areas".

Classification and types of hedgehogs

Although we usually imagine the typical hedgehog as being shaped like a balloon, the class Echinoidea It presents a great diversity. To better understand the Information about hedgehogsIt is useful to divide them into two large groups according to their morphology:

Regular Hedgehogs

These are the ones we all recognize. They have a spherical or semi-spherical shape and medium to long spines. They live on rocks and hard bottoms.

Example: The common or rock sea urchin (paracentrotus lividus), very abundant in Spain.
The case of the diademed hedgehog: Species like the Diadema africanum They possess very long, thin, and hollow spines. According to official sources, these spines contain irritating toxins and are very fragile, breaking easily within the skin..

Irregular Hedgehogs

They have a flattened or disc-shaped form and their spines are very short, almost like stiff fluff. They usually live buried in the sand.

Example: The so-called “sand dollars”.

The types of hedgehogs They vary drastically in their defense mechanisms and adaptation to the environment, occupying different ecological niches.

Food and behavior

There is a myth that hedgehogs are immobile animals, but they are voracious and active herbivores, primarily. browsers.

Diet: Their main food source is algae. They use their Aristotle's lantern to scrape the surface of rocks.
Defensive behavior: Scientific studies have shown that hedgehogs have complex behaviors. Researchers from the CSIC have observed that some species can detect the “chemical signal” (smell) of predators and actively flee when they feel threatened.Blanes Centre for Advanced Studies – CSIC).

Gastronomic and ecological importance in Spain

The sea urchin plays a crucial double role in our geography: it is an ecosystem engineer and a high-value culinary resource.

Gastronomic Value

In Spain, the consumption of sea urchins is a deeply rooted tradition, especially in winter, when their gonads (the edible orange parts) are more developed.

Asturias: Known as oriciosThey are a common delicacy.
Catalonia: The girls They are the stars of coastal cuisine in season.

Ecological impact

Ecologically, they control algae growth. If there is an overpopulation of sea urchins (due to a lack of natural predators), they can devastate seagrass meadows, creating barren areas known as "whiteouts." Conversely, their absence can cause algae to grow uncontrollably.

Nutritional value and health benefits

From a nutritional point of view, the Sea urchin is a low-calorie seafood and with a moderate fat content, very different from that of fish. Its edible part (the gonads) is light, but concentrated in nutrients, which makes it a food appreciated from both a gastronomic and nutritional point of view.

It is a good source of high biological value protein, necessary for the maintenance of tissues and muscle mass. It also provides healthy fatty acids, including omega-3 in moderate amounts, as well as essential minerals such as phosphorus and potassium.

Nutritional Information (Approx. per 100g of edible portion)

nourisher	Approximate quantity
Sustainable	385 kJ / 92 kcal
Proteins	10,3 gr
Total fat	2,8 gr
Saturated fatty acids	0,8 gr
Carbohydrates	6,3 gr
Sugars	0 gr
Potassium	197 mg
Football	128 mg
Iron	24 mg
Vitamin A	250 g

What to do in case of a sea urchin bite?

On rocky beaches, stepping on a sea urchin is a possible accident. Although painful, the species common on the peninsula are not usually dangerous, although their spines can cause infections as they are foreign objects.

If you suffer a sting, the general recommendation is to remain calm and act prudently:

Cleaning: Wash the affected area with soap and water to clean the wound.
Extraction: If the spines are sticking out and accessible, try removing them with sterilized tweezers very carefully so as not to break them.
Go to a professional: If the thorns are deep, many are embedded, or the area becomes inflamed, it is essential to go to a first aid station or health center. Do not attempt harsh home remedies or cut the skin to remove them.

Warning signs that you should see a doctor:

Intense redness or heat in the area.
Pain that does not subside or increases over time.
Appearance of pus or fever.

Frequently Asked Questions (FAQs)

Is a sea urchin a fish or a crustacean?

A: Neither. It's a echinodermwhich means it is related to starfish and holothurians (sea cucumbers).

Are the hedgehogs in Spain poisonous?

A: Most coastal species on the Iberian Peninsula do not inject venom dangerous to humans, although the wound can become infected. Species such as the Diadema africanum In the Canary Islands, they do have toxins in their spines that can cause more intense irritation.