What is the Evolutionary Advantage?

We have 5 fingers, not 4 or 6.

Starfish and Echindodermata, the other phylum in the deuterostomes, have pentaradial symmetry.

So I ask you, /sci/, what is the EVOLUTIONARY ADVANTAGE of five?

>>12
I know the Crown-of-thorns starfish can have 12-19 arms. They're becoming a real problem in coral reef ecosystems. They're like locusts. Since they're breeding so well, more arms must be an advantage, right?

Oh wait. They're also covered in poisonous spikes and so have no natural predators (except for the armies of pissed off scientists who are attempting to keep them for destroying the most diverse aquatic ecosystems on the planet).

http://en.wikipedia.org/wiki/Acanthaster_planci

That's about all my knowledge on starfish, but following a link at the top of that article goes to the giant sunflower starfish with 26 arms.