Well, after poking around in Borneman's book, as well as a few others, I think I've made a choice (okay, a guess, LOL).
I believe it's a Cladiella sp.
Unfortunately, most pics out on the net which are referred to as Cladiella really aren't. Here's one decent pic that I could find:
Cladiella is one of the soft corals which is often called a "Colt" coral. However, unlike most other colt corals, Eric Borneman describes Cladiella sp. as not soft, but "quite thick and durable". He also describes it as having "short stalks and stubby fingers", and as "heavy and lumpy when retracted".
That's about as close as I can get. The pics of Cladiella sp. in his book ("Aquarium Corals") look very similar to your specimen.
HTH!