What is Phylum Porifera in Classification of the Animal King?
Sponges are the simplest form of animals. Their bodies are not organized in any specific pattern other than masses of cells held together by a gelatinous matrix-the non-cellular material in which cells are embedded. As such, sponge cells are not organized into specialized tissues or organs that work together to perform a specific function.
The cells are not tied together through a nervous system. However, if the cells are fragmented into tiny clumps by passing the sponge through a wire mesh, the separated cell clusters can rejoin and reform the sponge body!
The anatomy of a sponge body is relatively simple. The sponge consists of a vessel-shaped body made of several layers of cells. The outer layer of flattened cells forms a covering called the epithelial wall. The interior of the vessel, or vase, is lined with distinctive cells called choanocytes, or collar cells. These choanocytes possess flagella, which beat independently and produce water currents through the sponge vessel.
A gelatinous matrix lies between these two layers and contains protein fibers known as spongin, sharp needles called spicules, and amoeboid cells. "Matrix" refers to the material substance in which the cells are embedded. The spicules may be of the needle-like or three-pointed variety, and are made of either silica or calcium carbonate. The spongin and spicules may function as either protection or support, or both.
Sponges are much like sacs that have lots of pores (hence the name Porifera) through which water is drawn. The collar cells, or choanocytes, help to circulate the water. This circulation brings both food for the sponge's cells and gases for exchange. Under the microscope, filtering structures can be seen on the collars that trap food particles, which are then absorbed by the collar cells. The food can then be transported to other cells by the amoeboid cells, which are able to roam within the gelatinous matrix.
Sponges are found mostly in marine habitats, with a few species found in fresh water. Sponges used to be harvested by the ancient Greeks and Romans for use in bathing. It is still possible to buy commercially harvested natural sponges.