Sea Urchins and Sand Dollars: Echinoidea

Physical characteristics: The body of long-spined sea urchins is somewhat flattened and is about 3 inches (8 centimeters) in diameter. The long, thin, black or white spines are 2 to 4 inches (5 to 10 centimeters) long. The shell and spines are fragile. There is a shiny blue ring around the anus.

Geographic range: Long-spined sea urchins live in the Indian Ocean and in the Pacific Ocean from Australia to Southeast Asia and along the western coast of South America.

Habitat: Long-spined sea urchins live in shallow water on rocks in sheltered areas of coral reefs, in sandy lagoons, and sometimes in sea grass beds. Darker urchins live in the open on sand; paler urchins live in crevices or in cloudy water.

Diet: Long-spined sea urchins eat algae.

Behavior and reproduction: Long-spined sea urchins hide during the day in rocky crevices but look for food at night. These urchins Long-spined sea urchins hide during the day in rocky crevices but look for food at night. These urchins are greedy grazers of algae. (Gregory Ochocki/Photo Researchers, Inc.) are greedy grazers on algae. When large numbers of the urchins die, algae grow rapidly and harm coral reefs. The shell color of long-spined sea urchins often changes according to changes in light. To protect themselves from predators, a variety of sea animals, such as shrimps and young fish, live among the spines of long-spined sea urchins. Long-spined sea urchins form groups when it is time to release eggs and sperm.

Long-spined sea urchins and people: The spines of long-spined sea urchins are poisonous and easily puncture human skin, often causing infection. Long-spined sea urchins protect coral reefs from overgrowth of algae.

Conservation status: Long-spined sea urchins are not considered threatened or endangered. ∎