Hi Nancy,

I believe you are referring to the "smooth arm starfish," quite commonly
found on the Gulf coast here. I've seen the 9 arm ones at least 18 inches
across before, and less common, the 5 arm ones. Check the photos for both at:

http://albums.photopoint.com/j/AlbumIndex?u=525417&a=6749555

Two other common starfish are pictured as well.

Scott
Florida