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Allostichaster polyplax (Family Asterinidae)

Spiny Seastar



The Spiny Seastar ranges from Long Reef at Collaroy near Sydney, around the southern shores to Rottnest Island in Western Australia, including Tasmania. It also occurs in New Zealand (NSW, TAS, VIC, SA, WA).


The Spiny Seastar is a small, long armed seastar that is seldom symmetrical because it can divide into two by autotomy. It normally has eight arms, but there may be 6 to 9. Several arms may be smaller then the others. It may grow to 30-40 mm across. Small spinelets are arranged in rows along the top surface of the arms. This is a diverse species. It may be uniform in colour, mottled, or banded. It is usually a subdued greyish-brown in colour. It may have shades or markings of brown, red, orange, cream or greenish grey. Its colours are never bright. It feeds on small molluscs and encrusting organisms.

Ecology/Way of Life:

The Spiny Seastar occurs on the undersurface of rocks in the low tide region and down to 130 metres depth. This is one of the most common of the southern Australian seastars. It is a species that prefers shelter and is found in crevices or inside dead shells. All seastars are carnivorous predators.

This seastar can reproduce itself by division, called autotomy, as well as by sexual means. After division each half can grow new arms to replace those lost. This must occur frequently, as it is rare to find a specimen with all its arms of equal length. This indicates that this seastar normally propagates by dividing into two. This process can occur at every stage in its growth. Occasionally a specimen may be found with only one long arm and seven small ones.

Preferred Image

Further Reading:

Bennett, I. (1987) W.J. Dakin's classic study: Australian Seashores. p. 349. Angus & Robertson.

Clark, H.L. (1946) The Echinoderm Fauna of Australia: Its composition and its origin. Carnegie Institution of Washington, Publication 566. p. 157.

Davey, K. (1988) A Photographic Guide to Seashore Life of Australia. p. 131. New Holland Press.

Edgar, G.J. (1997) Australian Marine Life: the plants and animals of temperate waters. p. 350. Reed.

Marine Research Group of Victoria. (1984) Coastal Invertebrates of Victoria: an atlas of selected species. p. 137. Museum of Victoria.

Shepherd, S.A. & Thomas, I.M. (1989) Marine Invertebrates of Southern Australia. pt. I. p. 417. South Aust. Govt. Press.


Text, map & photograph by Keith Davey.

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Images and Multi-media:  
Attached Image  
image/jpeg 17097 bytes Spiny Seastar
Distribution Map  
image/gif 969 bytes Distribution of Spiny Seastar

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