Phylum Porifera
The Sponges
The word porifera means “pore bearer”. The sponges are multicellular organisms that have bodies full of pores. These pores allow water to pass through them. This is how they obtain food because they collect the nutrients and food particles from the water. Sponges are found in marine areas like the ocean (in salt waters). Sponges are asymmetrical which means they have no definite shape. They have a jelly-like mesohyl between the the two cell layers. Sponges have no nervous, circulatory and digestive system. They rely on a constant water flow through their pores to obtain food and oxygen and to remove wastes. The water flows through the central cavity, where it deposits nutrients, and leaves through the osculum. Sponges reproduce sexually. They release sperm cells in the water that fertilize the ova. The fertilized eggs than from larvae that swim off to find a place to settle. There are four classes of sponges calcareous sponges, glass sponges, demosponges and the homoscleromorpha. Sponges absorb oxygen by diffusion from water into cells as water flows in their body. Carbon dioxide and other soluble waste products such as ammonia also diffuse. Sponges produce toxins that prevent sessile organisms from going near them. |