Poriferans are commonly referred to as sponges. An early branching event in the history of animals separated the sponges from other metazoans. Sponges are among the simplest animals on the planet, and it is believed that they evolved from the first multi-cellular organisms which eventually evolved into animals. The phylum Porifera represents the only phylum of the Parazoa branch of Kingdom Animalia--those without true tissues that diverged from the lineage shortly after the evolution of multicellularism from colonial protists.