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Superphylum Asterozoa
Phylum Asteroidea


  • Variable due to amount of yolk within the embryo.
  • Small embryos are 0.1 – 0.2 mm, whilst yolk rich embryos are up to 4 mm in diameter.


  • The embryos of sea stars.

Distinguishing characteristics

  • Development is through a bipinnaria stage that develops into a brachiolaria.
    • Bipinnaria larva.
      • Lateral lobes and arms not supported by skeletal rods.
      • Two bands of long, densely positioned cilia.
      • Coelomic pouches.
      • Posses a gut.
      • Feed on other zooplankton.
    • Brachiolaria (anchor larva).
      • Three brachiolar arms (1 dorsal and 2 ventral) and between them is an adhesive disk or sucker.
      • Eventually the disk or sucker fixes larval body to substrate.
      • Arms are short tubes that contain extensions of the larval coelom.
      • Tips of arms carry papillae which secrete a temporary adhesive.


  • Worldwide.


  • Asexual reproduction.

Additional notes

  • Asterias amurensis
    • Introduced seastar common to south-east Australia.
    • Thought to have been introduced from Japan in the early-mid 1980s via ballast water discharge.
    • Larval phase can last as long as 120 days at 10 degrees Celcius as determined from laboratory rearing studies (Bruce et al. 1995). Bipinnaria stage alone may live for 60 days.
    • Due to long development dispersive larvae could travel very long distances away from benthic adult population. This is a concern as adult Asterias amurensis feed voraciously on native benthic fauna, particularly bivalves, and have no natural predators in Australian waters.