Below is a simple example, which when combined with a good CV should be more than enough to get you an interview. Other than the quick summary suggested in the first paragraph you don't need to repeat the information on your CV. By all means say you enjoyed your final year project, but don't describe every experiment. Don't imply that you want to do it because you can't think of what else to do (it may be one of the most common reasons for doing a PhD, but no one wants to hear it) or that you'd really like to stay in/move to that particular city.
Dear Dr XXXX
I am writing to apply for your PhD studentship (XXXXXX), which I saw advertised on FindAPhD.com. I am currently a final year undergraduate at XXXXXX university and expect to graduate in July with a DEGREE AND GRADE in parasitology.
I would like to pursue a career in research because ..............……
Your PhD project is of interest to me because ..............
I look forward to hearing from you soon
Yours sincerely
XXX