The transition to Metazoa from a Protista World occurred before a large comet / plantesimal disintegrated and showered organic debris on the earth and moon 800 million years ago.
There is fossil evidence of keratose sponges at least by 890 million years ago. which suggests the the Ctenophora ancestors arose before that time, perhaps 1 Billion years ago. Specific extraterrestrial impacts at that time may correlate with major genetic change events in the biosphere that allowed the evolution of metazoa.
The above phylogram supports the ctenophora first hypothesis. See original article here http://www.plos.org/wp-content/uploads/2013/05/pone-9-9-olesen.pdf
Cnidaria – Hypothesis 101414a : Cnidaria evolved from symbiogenetic events with fungal microsporidian ancestors that possessed polar tubes.
Bilateria ( Protostomes and Deuterostomes)