What is this?

[sharuq1]

Considering where you got it I am guessing it is a leather, but it's polyps are in, so it's hard to tell just what type. As far as I know they had the following leathers: devil's hand, toadstool and possibly sinularia (finger leather). Leathers are pretty tough. If it's making a yucky mucous-like cover for itself put it in a bit higher flow to help it shed.

http://z.about.com/d/saltaquarium/1/...waxy_enhps.jpg

http://images.google.ca/imgres?imgurl=http://www.thelivingartaquarium.com/Softies/devils%2520hand.jpg&imgrefurl=http://www.thelivingartaquarium.com/leathercoral.htm&h=565&w=600&sz=81&hl=en&start=9&u m=1&tbnid=q7B66enQ3ifnrM:&tbnh=127&tbnw=135&prev=/images%3Fq%3D%2522leather%2Bcoral%2522%26um%3D1%26 hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-USfficial%26sa%3DX