I don't think this is a great argument. Crabs and lobsters have claws which are almost hand like. And Octopus have tentacles, which can be highly manipulative.

I don't think this is a great argument. Crabs and lobsters have claws which are almost hand like. And Octopus have tentacles, which can be highly manipulative. So those limbs must give those creatures an advantage even in water. It wouldn't be too much of a leap from those appendages to something as good as hands.