The origin of animal life is one of the key research topics in paleontology, the study of ancient life. That is because the evolution of animals is assumed to be the first big leap to multicellular complexity. While the first animals are thought to have been sponges, jellyfish-like, slug-like and worm-like body plans emerged during the Avalon Explosion and filter-feeding and grazing therefore seem to have been the main lifestyles during the ensuing Ediacaran.

With the Cambrian Explosion, slugs grew shells and became snails, some worms left their burrows and starfish-like, scorpion-like and fish-like creatures emerged. These formed the major phyla Porifera, Cnidaria, Mollusca, Annelida, Echinodermata, Arthropoda, and Chordata, respectively. Arguably the most interesting phyla are Porifera, Cnidaria and Echinodermata because unlike us chordates, they are not bilaterally symmetrical. This makes it hard for us to understand simple aspects of their body plan such as their incredible ability to regenerate and where they would wear their trousers.

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