15 Types of Sea Urchins: Species, Identification, and Photos

Sea urchins are typically viewed as spiky, black, spherical creatures. However, many may be surprised to discover this animal group's immense variety. Characterized by vibrant hues, differing spike lengths, and even flattened shapes, this diversified group of marine animals offers much to explore. Read on to learn more about these echinoderms and how to identify the different types of sea urchins.

Sea Urchin Classification

Sea urchins belong to the Echinodermata phylum, including fellow marine life such as sea stars, brittle stars, and sea cucumbers. They form the class Echinoidea with 13 orders and boast about 950 species. Displaying five-fold symmetry, sea urchins are equipped with hundreds of tiny adhesive tube feet, aiding movement.

Within this diverse group, two distinct subclasses exist: the symmetrical, globular Euechinoidea, which encompasses modern and irregular sea urchins, and the Cidaroidea, commonly known as slate-pencil urchins. 

The irregular echinoids, classified further as Atelostomata and Neognathostomata, include flattened sand dollars, sea biscuits, and heart urchins.

Globally, sea urchins are distributed across all oceans. From the intertidal seashore to depths reaching 16,000 feet, they continue to inhabit every depth zone. Learn about some of the most interesting species of sea urchins in the following sections.

Read more: Sea Urchin Facts.

15 Types of Sea Urchins

Quick link to the different types of sea urchin species:

1. Red Sea Urchin (Strongylocentrotus franciscanus)

The Red Sea Urchin is a sea urchin species found on the Pacific Coast of North America. It can reach up to 7 inches in diameter and feeds on kelp and various algae. 

Moreover, its body is covered with long, sharp spines colored in shades of red or burgundy, which protect it against predators. The spines also help them move around and enable the urchin to anchor itself to the ocean floor. Like most sea urchins, it can regenerate lost spines and other body parts.

Interestingly, the Red Sea urchin can live for 7 to 10 years, but scientists found a specimen that is expected to be around 200 years old. 

2. Green Sea Urchin (Strongylocentrotus droebachiensis)

Green Sea Urchins are small North Atlantic and North Pacific Oceans creatures. They range from lime green to almost ebony.

Green Sea Urchins use their short, sharp spines for mobility and defense. Green urchins feed on kelp and various algae types, helping maintain kelp beds. They also feed on slow-moving animals, residue, or dead organic matter for sustenance, allowing them to live up to 20 years. Their feeding organ, Aristotle's lantern, will enable them to scrape and chew their food.

Archaeological remains reveal how these edible sea urchins became a staple for the Native peoples of New Brunswick in Canada.

3. Pacific Purple Sea Urchin (Strongylocentrotus purpuratus)

The Purple Sea Urchin inhabits the intertidal zones of rocky landscapes from Baja California to British Columbia. As its name suggests, it sports spines that are deep purple.

This urchin can bore holes into rocks using its teeth, which allows it to seek refuge from predators and the relentless pounding of the waves.

Red and Purple Sea Urchins, both favorite food of Sea Otters, heavily graze kelp forests. When Sea Otter populations drop, Purple Sea Urchin numbers surge, leading to overgrazing and the destruction of kelp habitats. Therefore, a healthy balance between these animals is essential for the health of kelp forest ecosystems.

4. Pale Sea Urchin (Strongylocentrotus pallidus)

Pale Sea Urchins reside in diverse habitats, including sandy bottoms and rocky shores. They span from Norway to Russia and reach into the Sea of Japan.

Defining physical traits include their whitish to pale yellowish-green spines and incredibly light tube feet, often lighter than their spines. Each spine exhibits a flat surface with subtle ridges without obvious sculpturing.

5. Black Sea Urchin (Arbacia lixula)

The Black Sea Urchin lives in the shallow waters and rocky shores of the Mediterranean Sea and some parts of the Atlantic Ocean. It is known for its deep black hue and hemispherical form. Its black spines always maintain a sleek, erect appearance underwater.

Black Sea Urchin offers the potential as an abundant, natural source of astaxanthin. Farmed urchin eggs possess astaxanthin concentrations over 15 times higher than those in the wild⁴. This astaxanthin has broad beneficial applications, such as staving off diabetes and cardiovascular disorders and even bolstering the immune system.

6. Jewel Urchin (Lytechinus williamsi)

The Jewel Urchin is identifiable by its dense, short spines. Its pale brown body presents a brown-red stripe with white or deep green spines. You can also find purple tweezer-like structures called pedicellariae in between the spines.

This species of sea urchin is primarily found along Caribbean coral reefs, particularly in Panama, Belize, The Florida Keys, and Jamaica. Its habitats span from rock crevices to surfaces of table and lettuce corals.

Algae comprise most of its diet, which the sea urchin scrapes from rock surfaces using oral rasping mouthparts.

7. Variegated Sea Urchin (Lytechinus variegatus)

The Variegated Sea Urchin is a marine creature in the Western Atlantic Ocean. They inhabit shallow waters, preferring seagrass meadows and sandy or muddy bottoms. 

Their shells exhibit a range of hues from purple and green to dull red, often paired with white blotches. Characterized by short spines with a few longer ones, their colors vary even within a single spine. 

Common color combinations are green shells with either green or white spines, with white pedicellariae interspersed in between.

8. Stony Sea Urchin (Paracentrotus lividus)

The Sonty Sea Urchin inhabits the Mediterranean and northeastern Atlantic oceans. These regular sea urchins sport a greenish, flat, circular shell densely covered with sharp, predominantly purple spines. However, shades can vary from dark brown to olive green.

It feeds predominantly on algae and seaweed, and its body is covered in an array of short, sharp spines that help it dig soft rocks and provide some protection from predators.

9. Long-Spined Sea Urchin (Diadema antillarum)

The Long-Spined Sea Urchin, or Lime Urchin, inhabits coral reefs in the Atlantic Ocean’s shallow waters and coasts. Its thin spines can stretch up to four times the shell's diameter. 

Adult urchins predominantly exhibit black shells and spines, albeit with occasional intermixed lighter colors. Juveniles feature black and white banded spines. On death, the urchin sheds its spines, leaving only the test.

The Long-Spined Sea Urchin feeds on algae, which helps maintain the reef's health by preventing them from destroying the corals. 

The mass mortality of these types of sea urchins in 1983 led to unchecked growth of macroalgae that hinders coral development, furthering the decline of hard corals and negatively impacting coral reef resilience. Recovery was very slow. Unfortunately, another die-off event occurred in the U.S. Virgin Islands in January 2022³.

10. Common Sea Urchin (Echinus esculentus)

The Common Sea Urchin or European Edible Sea Urchin lives in the coastal areas of the northeastern Atlantic Ocean. 

It is primarily spherical yet slightly flat at both ends and displays a red or purple hue with white tubercles. Its shell is coated with a blend of short secondary spines and fewer, longer primary spines, usually white with purple tips.

While people eat sea urchins worldwide, this type of sea urchin isn't favored due to its white gonads. Other species with orange gonads are preferred⁵. Notably, it's not the actual eggs consumed but the male and female gonads.

11. Eccentric Sand Dollar (Dendraster excentricus)

The Eccentric Sand Dollar is an irregular sea urchin species in the northeastern Pacific Ocean. Its body is gray, brown, or purple, and it has a soft, velvety appearance and a unique pattern on its upper surface. The sand dollar can bury itself partway in the sand, standing up vertically for protection. 

This type of sea urchin is a suspension feeder, consuming crustacean larvae, copepods, diatoms, plankton, and detritus. Adults move by waving their spines, while juveniles use tube feet. They adjust their orientation for feeding and use pedicellariae, tube feet, and spines to catch prey. Adults grow heavier skeletons in strong currents, and juveniles ingest sand to stay grounded.

12. Fire Urchin (Asthenosoma varium)

The Fire Urchin lives in the Indo-Pacific region's coral reefs, rocky substrates, and sandy bottoms. 

This sea urchin is variously colored, including orange, red, brown, purple, or sometimes beige or shades of green. It features banded primary spines with paler bases and darker tips. The secondary spines are yellowish. On top, the primary spines are short, thick, bundled together, and sharp. Underneath, they adopt a trumpet shape.

Moreover, their spines are tipped with toxins, causing severe pain and swelling. They are nocturnal and regulate algae populations, preventing them from overgrowing and suffocating the coral reefs. 

13. Slate Pencil Urchin (Heterocentrotus mamillatus)

The Slate Pencil Urchin, also called Mine Urchin or Red Pencil Urchin, lives in the warm tropical waters of the Indo-Pacific region. It lives in coral reefs and rocky alcoves, where it can find food and protection. 

Regarding appearance, it typically showcases a bright red color, though some exhibit brown or purple shades. Its spines, bearing a unique white ring at the base and alternating light and dark rings, could differ in color from the body. They are rounded to triangular and taper toward the tip. Intriguingly, its red spines shift to a chalky pink hue at night.

Like other sea urchins, the Slate Pencil Urchin's spines comprise a network of magnesium calcite for fluid passage. The spines, dense at the base, become more porous towards the tip. 

However, it's unique for its sandwiched dense and porous spine layers. This structure allows a graceful failure, effectively dissipating pressure and preserving the bottom parts¹.

14. Heart Urchin (Echinocardium cordatum)

The Heart Urchin, often known as the sea potato, is a species with a discontinuous and widespread presence. It is found in the north Atlantic and west Pacific regions, as well as near Australia, New Zealand, South Africa, and the Gulf of California.

Its heart-shaped frame bears numerous furrowed, yellowish spines that primarily lean backward. With a flat top and an indentation upfront, the urchins showcase a fawn hue during their lifespan. However, their color tends to fade to white upon reaching the shore. 

This burrower digs into sandy floors, usually about 4-6 inches deep. It then remarkably creates a respiration channel up to the surface and a pair of sanitary channels at its back. All these paths are lined with mucus produced by the urchin, a clever adaptation to breathe while buried.

15. Flower Urchin (Toxopneustes pileolus)

The Flower Urchin lives in tropical and subtropical waters in the Indo-Pacific region. 

The flower urchin distinguishes itself with four types of pedicellariae, though two are abundant. The ophicephalous pedicellariae, similar to tube feet but with three small claws, keep the surface clean. Globiferous pedicellariae, resembling flowers, serve a defensive role against predators and parasites.

Their short, blunt spines blend beneath the floral pedicellariae. Colors range from white to purple with lighter tips. 

They produce two toxins: Contractin A, which interferes with nerve signal transmission and causes blood cell clumping², and Peditoxin, which results in lower body temperatures, muscle relaxation, sedation, and potentially death at high doses. Uniquely, the toxin is delivered through flower-like pedicellariae and not the spines.