How to confirm a new species

Here's an article on an intriguing topic. If you see some odd creature, or even collect one, how do you know it's new? Mark Siddall is a leech expert (someone has to be) who says, "I look at a new species name as a hypothesis." How do you confirm it? Comparison with type specimens of related species (there is still no agreement on what differences in DNA are sufficient to confirm a new species). How do you find new leeches? Seriously? Wade into tropical waters and wait. They find the researchers. Siddall once looked for a giant leech in Tennessee, as reported in Native American legend. No luck.