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Commonly Asked Questions

Species at Georgia Aquarium:
  • Echinometra lucunter: black boring sea urchin – Caribbean and Western Atlantic from Bermuda to Brazil, up to 5.9 inches in diameter (15 cm).
  • Diadema setosum: Pacific longspined black sea urchin – tropical seas, up to 24 inches (60 cm) in diameter.
  • Strongylocentrotus purpuratus: purple sea urchin – Eastern Pacific from British Columbia to Baja California, up to 4 inches (10.2 cm) wide and nearly 2 inches (5 cm) tall.
  • Strongylocentrotus franciscanus: giant red sea urchin – Eastern Pacific from the Gulf of Alaska to Baja California, up to nearly 7.5 inches (19 cm) in diameter.
  • Mespilia globulus: blue tuxedo urchin – Indo-Pacific, up to 2 inches (5 cm) in diameter.
  • Lytechinus variegatus: variegated sea urchin – Western Atlantic from North Carolina through the West Indies, common width of 3 inches (7.7 cm). Common height is 1.3 inches (3.2 cm).
  • Eucidaris tribuloides: slate-pencil sea urchin – Caribbean, up to 6 inches (15 cm) in diameter.
  • Echinometra viridis: green boring reef urchin – Caribbean, up to 1.9 inches (5 cm) in diameter and up to 1.2 inches (3 cm) tall.
  • Echinothrix calamaris: banded sea urchin – Indo-Pacific, 3 inches (8 cm) in diameter.
  • Genus: Diadema: long spine sea urchin – tropical seas, up to 24 inches (60 cm) in diameter.

Range / Habitat

  • Occur in oceans all around the world.
  • Mostly bottom dwelling, in shallow areas to deep sea floors. Generally found on rocky substrate.

Physical Characteristics

  • As echinoderms, sea urchins have pentaradial symmetry.
  • Skeleton made of calcite. 
  • Typically, the body is ovoid shaped with spines; the upper surface is domed and the underside is flattened.
  • The mouth has a complex structure made up of five calcium carbonate plates. It is referred to as “Aristotle’s lantern” because he was the first to describe it.
  • Spines and tube feet help the sea urchin to move or gather food.

Diet / Feeding

  • Scavengers; diet consists mainly of detritus and algae.
  • Typically grip hard substrate and feed on algae that coat the surface with the tentacles that surround the mouth.

Reproduction / Growth

  • Reproduce by spawning.
  • In some species, female will brood eggs between spines.

Conservation Status

  • Most species “Not Evaluated” on the IUCN Red List.

Field Guide to Seashore Creatures, National Audubon Society
Indo-Pacific Coral Reef Field Guide, Allen & Steene