Sand sifter starfish

[robinluvsbishies]

Why is my sand sifter starfish arched

 

[Pistondog]

Strange behavior, I have 4 in 3 tanks. Haven't seen this. They will curl up on the sand surface for a day.
How long has he been that way?

 

[Spieg]

I've seen mine do that when trying to move over something that stings their belly (urchin or some corals), but they flatten out again once they get to a clear patch of sand.

 

[Vette67]

I saw a video of someone’s sand siifter doing the same thing as it was releasing a milky cloud. It appeared to be breeding. It was arched in the exact same position. Is yours releasing anything into the water?