Can't tell for sure from the picture, but I think it might be a type of Porites. I've got a small patch in my tank that looks like what you have pictured, beige with little white polyps. Is it encrusting the surface of the rock? This is from the Hitchhiker FAQ section here at reefs.org:
"After my live rock cured, some very small polyps started to come out on some patches tan/ yellow/ brown colored tissue. They extend out about 1/8" from the skeleton. What kind of coral is this?
This could be a species of Porites. Porites is a common SPS (SPS - acronym for Small Polyped Scleractinia, sometimes called Small Polyped Stoney, refers to such genera as Acropora, Montipora, Pocillopora, Porites, Seri
atopora, Stylophora and others) coral on Indo-Pacific and Caribbean reefs. It can be encrusting, finger shaped, or dome shaped. It has tiny polyps and sometimes commensal fanworms (Spirobranchus giganteus). Porites usually requires strong illumination and wave action as they are most abundantly found in areas of high wave action and tidal flows. Similar to Montipora, Porites can be distinguished by much larger corallites (polyp walls) that are filled with septa ("teeth")."
-Bob
[ September 18, 2001: Message edited by: rBeOeBf ]