I just found this on another page. It's lenghty, but very informative. I hope it's fine to post here...
"The "sand-sifting stars" that we see in the petshops are all Paxillosid sea stars, almost all in the genus Astropecten or the genus Luidia. They are similar to other sea stars in that they have a water-vascular system that functions as a hydralic method to move their bodies around. They have the typical tube-feet sticking out of the bottom of the star, which they can retract when threatened, or move independently for locomotion or burrowing. Unlike most other sea stars, however, the end of each tube foot is usually pointed (rather than ending in the terminal sucker typical of most sea stars) for better anchorage in the sand (although there are a few sand-sifting stars in these general that retain the suckered tube feet). The have a unique type of skeletal element (bone-like ossicles called paxillae) that are umbrella-shaped, and have a bunch of mobile spines (almost like a miniature urchin if you were to look at them under a microscope) across the top. These tiny spines allow the star to clean sand off of itself when above the surface, and the umbrella-shaped ossicles are usually dense enough to cover the entire upper surface of the sea star, so that they are still able to extend the gill-like filaments (papulae are the sea star equivalent of gills in fish) to allow the animal to breath when buried in the sand. They also usually have a distinctive row of marginal spines around the edge of the star that are used for prey capture in some species, and presumably function for defense as well. Most species in these genera are very fast for a sea star, and when stimulated some species can crawl at speeds as high as 75 cm/sec! Both Astropecten and Luidia are found almost exclusively in soft, sandy bottom habitats where they burrow through the sand for protection and in search of prey (hence the name sand-sifting sea stars).
And this is where we get to the part that you probaly don't want to hear, Bob. They are almost all voracious predators that consume a wide variety of vertebrate and invertebrate prey. They are most active at dusk and dawn, when the light regime is subdued, but their foraging behavior is likely to be somewhat disrupted by the fact that few aquarium lighting systems have a dusk and/or dawn setting (most of us just turn the lights on or off). They prefer to feed at night to during the day, and the reason that most people don't see any problem with these animals is that they eat things while we're asleep and not really watching the tank. The stars appear to have chemosensory abilities that allow them to discriminate among prey, and there have been a couple of studies showing that they will adjust their feeding behavior and preferentially eat certain prey in response to changes in prey density. Some species actually ingest their prey, while others simply use their spiked arms to trap the prey below the sand surface, and secrete digestive enzymes to turn the captured critters into an easily ingested paste.
Regardless of their method of feeding, they are all pretty voracious feeders. In fact, gut-content analyses of 100 sea stars caught in the wild revealed that there were 91 different species of invertebrate prey eaten recently by these stars! The most common prey items they ate in the wild were snails and bivalve (clams & mussels) molluscs, but they also ate a large number of other echinoderms (including small sand dollars, sea stars, urchins, brittle stars, and sea cucumbers), polychaete worms, small crustaceans (including shrimp, crabs, and all the various 'pods), dead or foolishly slow fish, and some small cnidarians (sea pens, sea pansies and anemones that dwell in sandy areas). They can eat an incredible amount of food for a small star, and individual stars have been found with as many as 70 brittle stars in their stomach at one time!
We have large shallow holding tanks (~10 ft by 2.5 ft) here at UC Davis that we use for invertebrate labs, and I had a couple of them set up with nice sandbeds of local animals to use for display in the labs. The addition of a few Astropecten to that large bed eliminated all visible life (including snails, worms, clams, heart urchins, and sea pansies) from the sandbed in only a couple of weeks...
Kinda makes you wonder how long it will take to make a serious dent in the sandbed population of your 45 gallon tank, doesn't it?"
I found it on this other
BBS .
Peace
