Sand-sifting sea stars in the genus Astropecten, a group distinguished by flat, paxillaeted bodies bearing prominent marginal arm plates and lateral spines, are not rare on the northern and eastern shores of Singapore. The animals appear to favour sandy flats with loose, unconsolidated sediments, unlike another 'common' sea star which thrives in somewhat siltier substrates. Prey availability may be another factor for their occurence, as Astropecten is a benthic predator that lacks the ability of more advanced asteroids to evert its stomach and 'graze' on organic matter or sessile growth. Instead, the astropectinids chase discrete prey, which they swallow whole before expelling the indigestible portions.
The sea stars are catholic eaters, having been recorded to consume fish, crustaceans, worms, ascidians and other echinoderms. Ciliary feeding, in which edible matter is trapped in mucus and transported to the mouth, is also performed, but this is likely an option for lean times. Where the hunting is good, the stars' streamlined form confers a pace that probably surprises motile prey and their slender central disc belies a buccal cavity with the disturbing ability to expand and engulf larger or a greater number of food items. Small molluscs, however, are their preferred quarry and the presence of date mussels and button snails may account for the stars' abundance or absence in otherwise suitable habitat.
Tiny but still visible paxillae, parasol-like structures that help maintain a flow of water over the respiratory papullae, on the dorsal surface and long spines that work like the teeth of a spading fork arm the stars for a dig through sand. Aided by dextrous tube feet, the animals glide over the seabed with disconcerting speed and sink out of sight with near-equal ease to pursue buried prey or avoid trouble. Two possible species, one plain and the other patterned, are often seen at shores such as Changi and Chek Jawa, but a quite different Astropecten was spotted yesterday at a coast beyond the reach of casual beachcombers.
With an orange underside and nearly twice as wide as its commoner kin, this individual was a rich reddish-brown, turning paler on the fringes, with marginal plates in a pretty shade of blue. Darker pigments surrounded the base of short spines on the upper surface of the plates, tracing a prominent rim of dashes just behind a perimeter of long primary spines. Almost as fleet-footed as its smaller cousins, the star employed a curious means of burying itself: the primary spines on each arm would be folded like the leaflets of a sensitive mimosa, firstly at the base, followed by those at the tip in a domino fall of slow motion. The extremities then dug in, causing the surrounding grains to cave in as if the seabed were sucking the star into its heart of darkness and consuming its children before the tide comes in and time runs out for this coast of reclaimed fortunes.