Phylum Porifera: Sponges

Sponges are regarded as the most primitive of animals because of their 'simple' body plans, having a multicellular grade of construction but without actual tissues or organs, yet studies of this oldest of metazoan groups have contributed a great deal to our understanding of life on Earth. For example, the discovery of complex immune and cell-aggregation systems in sponges has led to better understanding of the cellular processes of higher organisms and, in particular, the nature of cell surfaces as active agents in cell and tissue recognition (Bergquist 1994). Their fossil record dates back about 600 million years (Finks 1970; Li et al. 1998).