How do leeches swim?

The leeches' body is, "dorso-ventrally flattened". Meaning they are flat from top to bottom. Leeches are able to change their appearance from long, snakelike bodies to short, squat and contracted in an instant. This is one of their primary defensive reactions. Leeches swim with their bodies extended. The rear of the body is wider and flatter than the front. This paddle like appearance makes the leech a competent swimmer.