A sea urchin is a spiny, spherical marine invertebrate belonging to the class Echinoidea. As echinoderms, they are related to starfish, brittle stars, and sand dollars.
Appearance and Features
- Physical Structure: A sea urchin’s body is protected by a rigid, spherical shell known as a “test,” which can range in diameter from 6 to 12 centimeters in adults.
- Spines: Their bodies are covered with numerous spines that vary in length, thickness, and toxicity depending on the species. These spines serve as defense against predators and aid in movement.
- Mouth: The mouth is located on the underside of the body. It contains a complex, jaw-like structure called an “Aristotle’s lantern,” which is equipped with five perpetually sharpening teeth for scraping algae and other food.
- Movement: Since they cannot swim, sea urchins move slowly along the seabed using their spines and small, suction-cupped tube feet.
Habitat and Diet
- Habitat: Found in every ocean worldwide, sea urchins inhabit a variety of environments, from shallow intertidal zones to ocean depths of over 7,300 meters. They prefer rocky and coral bottoms.
- Diet: Although primarily herbivores that scrape algae from surfaces, sea urchins are omnivores. They may also consume carrion, sponges, mussels, and other small organisms.
- Ecological Role: Sea urchins are crucial to marine ecosystems. They help control algae growth and serve as a food source for predators such as sea otters, lobsters, and crabs. An overabundance of sea urchins, however, can damage kelp forests by overgrazing.
Culinary Use
- Delicacy: The edible part of the sea urchin is its gonads, known as “uni” in Japanese sushi. It is considered a delicacy in many seafood cuisines.
- Taste: Uni has a unique, delicate, and minerally flavor, sometimes compared to oysters.
- Nutrition: Sea urchin gonads are rich in protein, minerals (calcium, zinc, iron, magnesium), vitamins (B12, A, E), and heart-healthy omega-3 fatty acids.
