Nerve cells may have evolved in animals twice

Ctenophores, also known as the "comb jellies", are an ancient phyla of animals. They have no HOX genes, at least some of which are present in every other animal except themselves and sponges. They lack many of the basic immune system adaptations common to all other animals, including sponges. » 5/27/14 10:16am 5/27/14 10:16am