Alternation of generations
In some animals, there is a life cycle with different diploid stages. This has sometimes mistakenly been called "alternation of generations", but is quite different from what happens in plants and some protists. The most common case is that there are two distinct generations, where only one has sexual reproduction.  Animals where it has been found include  the Cnidaria and the Tunicates. The images on the right show the case of jellyfish: The medusa looks different from the polyp; they are different phenotypes. Only the medusa reproduces sexually.