Sea Urchin, Echinoderm, Rock Sea Urchin, Purple Sea Urchin

Sea urchins are marine invertebrates belonging to the class Echinoidea. They are characterized by their spherical or elongated bodies covered in spines, which provide protection and aid in movement. Their rigid skeleton is made of calcium carbonate plates. They lack a distinct head and have a complex feeding structure. Sea urchins play a vital role in marine ecosystems, influencing algal populations and serving as a food source for various predators.

Sea urchins inhabit a wide variety of marine habitats, including rocky shores, coral reefs, seagrass beds, and sandy or muddy bottoms. They are commonly found in shallow coastal waters, but can also be found at greater depths. Specific species have varying preferences, with some preferring highly exposed rocky areas, while others thrive in calmer, more sheltered environments.

Typically 1-3 years, but some species can live up to 5 years or more under ideal conditions.

Sea urchins begin as free-swimming larvae called plutei. These larvae feed on microscopic algae and undergo several developmental stages before settling onto the seabed and transforming into the juvenile urchin. As adults, they primarily feed on algae, detritus, and small invertebrates using their specialized feeding apparatus, known as Aristotle’s lantern. Sea urchins reproduce sexually, releasing eggs and sperm into the water for fertilization. Predators include sea otters, sea stars (particularly sunflower stars), fish, crabs, and birds. They are important in maintaining balance in the marine ecosystem, controlling algae growth and serving as a food source for other organisms.

Sea urchin gonads (often called 'uni') are a delicacy in many cultures, particularly in Japan. They have a rich, buttery, and slightly sweet flavor. Harvesting and consumption is tightly regulated in many regions to prevent overfishing. Consumption is not universal and some may experience allergic reactions.