Sea urchins are typically found in areas with rocky bottoms, from shallow waters to deep sea floors, and occur in oceans all around the world. Species can range from 1.9 inches (5 cm) in diameter to 24 inches (60 cm) in diameter. Sea urchins belong to the phylum Echinoderms and have pentaradial symmetry. Typically, the body of sea urchins is ovoid shaped with spines; the upper surface is domed, and the underside is flattened.
  • Size

    1.9 inches to 24 inches (5 - 50 cm)
  • Diet

    Diet consists mainly of detritus and algae
  • Range

    Cceans all around the world
  • Habitat

    Ocean floors

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.

Animal Fact

A sea urchin’s skeleton is made of calcite.

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.

Range / Habitat

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

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.

Additional Information

  • Approximately 940 species of echinoids living today; typically grouped as “regular” or “irregular.” Sea urchins are regular echinoids; irregular echinoids are sand dollars.
  • Moves by way of a water vascular system and tube feet.

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.

Sources

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