sea urchin needles?

[macfish]

I have been trying to figure out what is laying on the bottom of my tank for the last several days. They are about 3/4 to 1 inch long. Look very much like sea urchin spins but there are no urchins in my tank. They seem to have multiplied in the last week. Colorartion varies from white to grey to multi white with brown stripes. Anyone have any ideas?

 

Thanks.