Phylum Echinodermata > Class Stelleroida > Subclass Asteroidea
Common sea star
Archaster typicus
Family Archasteridae
updated Jan 14

if you learn only 3 things about them ...
They are no longer common on all our shores.
Their method of mating is unique among sea stars
They use water to pump up their bodies. Don't remove them from water for too long.

Where seen? Despite its name, this elegant sea star is no longer common on all our shores. In the North, Chek Jawa used to be the only place where it was seen in large numbers. But following massive flooding in Johor in early 2007, there were mass deaths among these animals (more about the mass deaths on the Chek Jawa project blog). It is not no longer found on Changi or the East Coast. But it remains the most commonly encountered sea star on Southern shores. Generally in shallow sandy or silty areas near seagrasses and mangroves.

Features: Adults diameter with arms to about 12-15cm. Smaller juveniles are rarely seen. Body somewhat rounded (not flat). Arms long and tapered to a sharp tip, and edged with short flat, blunt spines. Most have five arms, but those with three, four and six arms are sometimes also seen.The underside is pale, with large tube feet tipped with suckers. Colours and patterns on the upperside are highly variable in shades of greyish blue, to brown and beige.

Sometimes confused with the Eight-armed sand star (Luidia maculata). The Eight-armed sand star has, well, eight arms and large tube feet with pointed tips. While most Common sea stars have five arms (although some may have six), and all have large tube feet with sucker-shaped tips.

What does it eat? According to Schoppe, it feeds on detritus, decaying plants and tiny animals. To eat, a common sea star sticks out its greenish 'stomach' through its mouth on the underside. The 'stomach' spreads out to mop up any edible titbits on the sand surface.

Uncommon mating ritual: Sea stars of the genus Archaster have a unique mating behaviour. The male, which is usually smaller, seeks out a female during the breeding season. He then moves on top of her, his arms alternating with hers. Their reproductive organs do not actually meet. Sperm is merely released by the male when the female releases her eggs, for external fertilisation.

This behaviour is believed to increase the chances of external fertilisation. So much so that the males do not need to be large and are thus usually smaller than the females, a rare gender difference among echinoderms. The only other sea star known to practice this kind of mating behaviour is the closely related Archaster angulatus.

Juveniles are found in prop roots of mangroves and gradually inhabits sandy shores, seagrass areas and shoals as they age, where they are burried slightly in the sand.

Living on a star: A tiny parastic snail (Parvioris fulvescens) is said to be sometimes found on the underside of the common sea star. Here's some of the parasitic Ulimid snails (Family Eulimidae) seen on our Common sea stars.

Is our sea star special? According to the Singapore Red Data Book, the form found in Singapore is larger than other examples elsewhere in the west Pacific and may be a distinct variety of subspecies.

Status and threats: Although plentiful in the past, common sea stars are now listed as 'Vulnerable' on the Red List of threatened animals in Singapore due to habitat loss and overcollection. Their mating behaviour suggests that a certain population density is required for them to be able to reproduce successfully. In the past in Singapore, the common sea star was often collected as a teaching aid in zoology and biology. This practice can threaten the population if it results in overcollection.

Various colours and patterns,
sometimes four or six arms
Chek Jawa, Dec 03


The greenish stomach sticks out through the mouth to 'mop up' edible bits on the ground.
Chek Jawa, Feb 02


This pair of sea stars are in 'mating' position.
Chek Jawa, Nov 04


Arms can become flexible to turn
themselves over if accidentally flipped.

Chek Jawa, Mar 05

Pulau Hantu, Jun 09

The white structure is the madreporite.


A four-armed specimen
Chek Jawa, Nov 06

Wiith seven arms.
Cryene Reef, Jul 10

With six arms.
Kusu Island, Feb 07


A mating mess?
Chek Jawa, Mar 05

Small male on top of larger female.
Kusu Island, Sep 10

A distintegrating sea star
due to massive floods.
Chek Jawa, Jan 07


Regenerating new arms.
Tanah Merah, Oct 09

Regenerating new arms.
Tanah Merah, Oct 09

Parasitic snail on arm, not often seen.
Pulau Hantu, Jul 08

Common sea-stars on Singapore shores
Photos for free download from wildsingapore flickr

video clips and more photos of common sea stars at various locations in Singapore


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