Ctenophores and Cnidaria both have nerve and muscle cells, but Ctenophores lack Hox genes that occur in both Cnidaria and Porifera. What is the most likely explanation?
a. Porifera diverge from a common ancestor before nerve and muscle cells evolved, then Cnidaria and Ctenophores absorbed viral genomes containing Hox genes from plasmids contained within their environment.
b. Hox genes were deleted from the Ctenophore genome after Ctenophores diverged from a common ancestor with Cnidaria, and Porifera developed nerve and muscle cells.
c. Hox genes developed in a common ancestor of Cnidaria and Porifera after it diverged from an ancestor in common with Ctenophores, then nerve and muscle cells developed via parallel evolution.
d. Hox genes are produced by mitochondria; Porifera lack mitochondria, and therefore cannot contain Hox genes. The presence of nerve and muscle cells is entirely unrelated and irrelevant.
c. Hox genes developed in a common ancestor of Cnidaria and Porifera after it diverged from an ancestor in common with Ctenophores, then nerve and muscle cells developed via parallel evolution.
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