The Hecatoncheires was the collective name given to three monsters; (Briareus, Cottus and Gyges) who were the children of Gaia and Uranus. They were not only known for their frightful enormity, but also for their ghastly arrangement of one hundred arms and fifty heads. Even Uranus was so taken back by their ugliness that he decided to push them back into their mother’s womb. On failing to do so, they were subsequently banished to the underworld of Tartarus.
This is a very creepy creature and is probably going to be a very difficult challenge. I imagine that it will have to be an invertebrate of some kind, maybe a mollusk or even an advanced sponge. I also really doubt all appendeges will be functional. How could a Hecatoncheires appearing species realistically evolve.
A list of all of the Anatomically Correct questions can be found here, suggestions for future question are welcomed;