FTP, name this phylum that includes hydra and jellyfish.
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.
It was the dominant phylum in the late Precambrian period.  
Cnidaria or Coelenterata