PORIFERA
Porifera are divided into three classes: Calcarea, Glass Sponges, and Demosponges. They all obtain oxygen through oxygen diffusion. This allows oxygen to pass from the water into the body of the Porifera to be used as nutrients. No organs are necessary in the respiratory system.
Sponges
The sponge fulfills the requirements for respiration by diffusion alone: a large, moist area for gas exchange in the form of cells that are never more than 1mm away from the site of exchange. Gas exchange occurs in a sponge by simple diffusion across each cell membrane. Gas exchange always takes place by diffusion, in which the gases move from where they are most concentrated to where they are least concentrated, carbon dioxide moving in one direction and oxygen in the other. In human beings this occurs across the alveolar-capillary membrane in the lungs.
Tube Sponge
The elegant, tubular branches of this beautiful sponge are easily torn, and so it occurs only on deeper reef slopes, where wave action is minimal. It sometimes grows as a single tube, but it is more often seen as bunches of tubes joined at the base. The tips of the tubes are translucent and slightly rolled in. The color of this sponge is usually pinkish violet, although some specimens are pinkish blue. When this sponge releases sperm, it resembles smoking chimneys
Vase Sponges
Sponges from this group are mainly found in the region surrounding the Caribbean islands and the coast of Florida, USA. The vase sponges can grow up to 40-60cm in diameter. This kind of sponge is found in different shades of brown, red and purple. Scientific name of this sponge is Ircinia campana.
- Azure Vase Sponge: The Azure Vase Sponge is characterized by a tubular and vase-like shape. Its outer surface is marked with pits and network of grooves. These sponges can grow up to 30cm in length. Pits found on the surface of Azure Vase Sponges are 0.5 to 1cm in diameter.
- Strawberry Vase Sponge: These sponges are mainly found in areas surrounding the Caribbean islands. The strawberry vase sponges are found in oceans at a depth of 15-40 meters.
Barrel Sponge
Giant barrel sponges grow large enough to fit a person inside. Their hard surface is deeply ridged, but their rim is thin and delicate. The barrel sponge belongs to the Demospongiae, the largest class of sponges, containing about 95 percent of sponge species. The skeleton of sponges in this class is made from both scattered spicules of silica and organic collagen called spongin. An almost identical barrel sponge, Xestospongia muta, occurs in the Caribbean.