Multicellular and Tissue Levels of Organization

Poriferans are commonly referred to as sponges. An early branching event in the history of animals separated the sponges from other metazoans. As one would expect based on their phylogenetic position, fossil sponges are among the oldest known animal fossils, dating from the Late Precambrian.

Reference:

  • Miller, A.S. and Harley, J.B., 1999 & 2002 . Zoology , 4th and 5th Edition (International), Singapore:McGraw Hill.