What did the earliest animals look like? Chromosome analysis resolves debate about sister group of all animals. It's comb jellies, not sponges
Surprisingly, genome comparisons have failed to resolve a major question in animal evolution: Which living animals are the descendants of the earliest animals to evolve in the world's oceans? Scientists performed a detailed chromosomal analysis that comes down definitively in favor of comb jellies, or ctenophores, as the most recent common ancestor of all animals, or the sister taxa to all animals. Sponges evolved later.
Source: sciencedaily.com