well, according to religion there isn't such a thing as evolution.
So I speculate that god must have given them opposable thumbs, when they prayed to him and asked for it.
problem was that the tubeworms were a collection of contradicting Christians (a couple protestants, a catholic and a Mormon), so only the Mormon worm got his wish.
they rest were labeled as blasphemous and were condemned to an eternity living at the bottom of the ocean, near those super hot and toxic thermal vents...
It was quite sad for them to see their brethren shipped off to the vacuum of space, to live.
I mean, shit... since we are having an intellectual conversation here....