This phylum includes sponges. They are simple cell-grase animals that feed by filtering water and often have needles of silica or carbonate to help support the body and to deter predators.

Classes:

Demospongia

Hexactinellida

Calcarea

Archaeocyathids

For more information:

http://www.ucmp.berkeley.edu/porifera/porifera.html

http://www.palaeos.com/Invertebrates/Porifera/Porifera.htm