Diadema refers to a genus of sea urchins known for their long, slender spines. These marine animals are typically found in tropical and subtropical oceans, often inhabiting coral reefs. They play a crucial role in the ecosystem by grazing on algae, which helps maintain the health of coral reefs. The most well-known species within this genus is Diadema antillarum, commonly called the long-spined sea urchin. This species has faced significant population declines due to disease and environmental changes, impacting reef health. Conservation efforts are underway to restore their populations and protect marine biodiversity.