Select the odd one out w.r.t. fertilization :

In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water), i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation. If syngamy occurs inside the body of the organism, hence the process is called internal fertilisation e.g., Spirogyra.