Octopus FS has bumps that mostly are close to the tentacle, rather than mostly on a branch that extends out from the tentacle.
In the pic, there is a "normal FS" on the right, and an "octo FS" on the left.
I think that the "octo" version mostly grows in a wall form, but I have seen a few branching one as well.
I think that they may be a separate species than "normal frogspawn" but still it is a ploy to mark up the price of something that is different. One LFS that is near me has a single head of green/green octo FS that is about 6-8" in diameter. It does not split, just keeps getting more and more round.
I will admit that I fell for the ploy. I normally will pay $10 for a head from a hobbyist, and $20 for a head from a LFS. I looked for a green/green octo FS for three months before I bought a large head of it for $60 last summer. Now it is starting to split and I can clearly see 3 heads starting to form (must be a branching form

)
Just to put it in perspective, one half of my 75g is devoted to Euphyllia. I think I have between 75-100 heads of all different colors of hammer and FS. There are only a few color patterns that I have seen that I do not have.
dsoz