Diadema antillarum, also known as the lime urchin, black sea urchin, or the long-spined sea urchin, is a species of sea urchin in the family Diadematidae. This sea urchin is characterized by its exceptionally long black spines. It is the most abundant and important herbivore on the coral reefs of the western Atlantic and Caribbean basin.

Diadema antillarum, the long-spined sea urchin, is an ecologically important species in Caribbean coral reef habitats where it controls algal growth and coverage and helps keep reef surfaces clear for corals to grow and settle. Sea urchins in the genus Diadema serve critical ecosystem functions within coral reef environments.

Diadema antillarum (Spiny Urchin) is a species of echinoderms in the family Diadematidae. They are native to Atlantic Ocean. Dead Spiny Urchin form shallow marine sediment s. They are nocturnal omnivores. Individuals can grow to 28 mm. They have sexual reproduction.

Diadema antillarum, also known as the long-spined sea urchin, is one of the most important herbivores on Caribbean coral reefs because they eat algae, reducing algal overgrowth on the seafloor, which in turn provides reef area for coral growth.