Why are the alien creatures called mimics?

In the book "All you need is Kill", the alien creatures called Gitai (ギタイ in Katakana, 擬態 in Kanji) which translates to English is Mimicry. More details about the alien are in the book. I never read it, so can't help.

The book said they mimicked starfish. The mimics were sent from another planet to modify the Earth so aliens who needed elbow room could colonize it. The mimics ate whatever they could find and excreted material that was poisonous to Earth life. They evolved to combat earth forces and reset time whenever they lost a battle so they could win later on.

wonder the same thing