Why might introduction of exotic species disrupt an ecosystem?

What is the phylum of soft bodied animals with a true bosy cavity and a three part body consisting of a foot visceral mass and a mantle

What molecules will be best used to compare different species with the exact same sequence of amino acids? why would two species have the same protein even if the molecules in question is different? (hint: transcription to translation to protein).

What are some natural processes that represent physical and chemical changes?