For a given gravity, temperature, salinity and life cycle there are a single best and more efficient solution for moving and survive. Evolution will prune all

For a given gravity, temperature, salinity and life cycle there are a single best and more efficient solution for moving and survive. Evolution will prune all the bad paths so with enough time will go closer and closer to the more efficient design, Crabs evolved to protect their delicate eggs from mud and debris. You need that if you pass most of your time hiding buried in the mud. This means also that with enough data about other planets we could even made a raw guess the shape of creatures that could live there.