Sea stars occur in ocean environments worldwide.
  • Size

    Range in size from less than .8 inches (2 cm) to more than 3 feet (1 m) in diameter.
  • Diet

    Diet varies depending on species.
  • Range

    Variety of habitats from shallow sandy bottoms and cold rocky environments to the bottom of the sea floor.
  • Habitat

    Marine habitats.

Physical Characteristics

  • May range in size from less than .8 inches (2 cm) to more than 3 feet (1 m) in diameter.
  • Body is comprised of a central disk with arms radiating outward.
  • External surface of the body is covered in claw, clamp, wrench or beak shaped structures called pedicellariae.
  • Internal calcite skeleton.
  • Move by using their water vascular system. Internal muscle contractions squeeze fluid to the tube feet, which then elongate. Cilia within the epithelium of the water vascular system move the water. The end of the tube feet have suckers, which chemically adhere to the substrate. Another chemical bond is secreted to release the tube feet.
    • Sea stars living on soft bottom substrates have pointed tube feet (rather than suckers) to help them move.
    • Brittle stars move by wriggling their whole arms rather than tube feet.

Animal Fact

Most species of sea stars have five arms, but some species may have as many as 40 arms.

Diet / Feeding

  • Diet varies depending on species; consists of gastropods, bivalves, barnacles, marine worms and other invertebrates.
  • Mainly scavengers and carnivores.
  • Feeds by grasping prey with its tube feet, then turning its cardiac stomach inside out through the mouth. The sea star will then secrete digestive enzymes onto prey to break it down. Once the prey has been sufficiently digested, it will then be sucked up by the sea star and the stomach will retract back into the body through the mouth.
    • Some species of sea star are suspension feeders. Mucus on the body surface captures plankton and organic detritus. Cilia move the captured plankton and detritus to the mouth.
    • Very few species use their numerous pedicellariae to capture prey.

Range / Habitat

  • Occur in ocean environments worldwide.
  • Primarily found in marine habitats with very few species being found in brackish water.
  • Benthic, or bottom-dwelling. Found in a variety of habitats from shallow sandy bottoms and cold rocky environments to the bottom of the sea floor.

Reproduction & Growth

  • Sexual reproduction occurs by spawning.
    • Some species are hermaphroditic.
  • May also reproduce asexually by dividing the central disk.
  • Larvae are planktonic and bilaterally symmetrical. Adults are radially symmetrical.
  • No parental invest beyond fertilization.
    • Some hermaphroditic species brood their young. Typically, brooding species are found in environments that are harsh for the larvae.

Conservation Status

  • Many species of sea stars are considered keystone species within their environments.
  • Increased numbers of sea stars can damage coral reefs and commercial oyster beds.
  • Sea star wasting syndrome (SSWS) caused mass die-offs along much of the North American Pacific coast beginning in 2013.
    • Pisaster ochraceus and at least 20 other species of sea star have been affected.
    • Sea star wasting syndrome is a general description of a set of symptoms. Typically, lesions appear in the ectoderm followed by decay of tissue surrounding the lesions, which can lead to eventual fragmentation of the body and death.

Additional Information

  • Around 2,000 species of sea star have been described throughout the world.
  • Most species have five arms, but some species may have as many as 40 arms.
  • Brittle stars are not considered true sea stars.
    • True sea stars lack the sharp demarcation between the arms and central disk.
  • Some species of sea star may live up to 35 years.
  • Many species can regenerate lost limbs as long as the central disk is intact.

Species at Georgia Aquarium

  • Bat star (Asterina miniata) – U.S. Pacific coast from Alaska to San Diego, diameter can reach 12-16 inches (15-20 cm).
  • Brittle star (Class: Ophiuroidea)
    • Ophioderma brevispinum: short-spine brittle star–Caribbean, up to12 inches(30 cm) in diameter.
    • Ophiocoma echinata: spiny/black brittle star–Caribbean, up to 8inches (20cm) in diameter.
    • Ophiarachna incrassata: green and gold brittle star–Indo-Pacific, up to 20 inches (50 cm) in diameter.
  • Brown spiny sea star (Echinaster spinulosus) – western Atlantic from Florida, the Gulf of Mexico and southern Bahamas to the northern coast of South America. Reaches a diameter of 4-5 inches (10-13 cm).
  • Caribbean spiny sea star (Echinaster sentus) – western Atlantic from North Carolina to the Bahamas and West Indies, maximum length of 7 inches (18 cm).
  • Chocolate chip sea star (Protoreaster nodosus) – Indo-Pacific, reaches 16 inches (40 cm) across.
  • Mottled sea star (Evasterias troschelli) – Bering Sea to south and central California, can reach about 22 inches (56 cm) in diameter.
  • Ochre sea star (Pisaster ochraceus) – eastern Pacific from Alaska to Baja, California, diameter of 6-14 inches (15-36 cm).
  • Pink sea star (Pisaster brevispinus) – Pacific coast from Alaska to southern California, can reach 20-28 inches (51-71 cm) in diameter.
  • Rainbow sea star (Orthasterias koehleri) – Aleutian Islands south to central California, can reach 20 inches (50 cm) in diameter.
  • Vermillion sea star (Mediaster aequalis) – eastern Pacific from Alaska to Baja, California, 7 inches (18 cm) in diameter.


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