In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: It was the dominant phylum in the late Precambrian period. Creatures in it phylum have bodies consisting of an internal gastrovascular cavity, a soft, pliable middle body layer known as the mesoglea, and an external dermis. Its members often live in two phases, a sessile, asexual polyp and a free-moving, sexual medusa. FTP, name this phylum that includes hydra and jellyfish.
A:
Science