The Circulatory System of the Porifera
The porifera (sponges) are the some of the longest existing and some of the simplest multi-cellular animals. They are among the oldest animal fossils and are bottom dwelling invertebrates. The word porifera literally means "pore-bearing" There is a possibility that sponges have separated from other metazoans because of an early evolutionary branching event. Ever since, sponges have taken a completely characteristic and unique evolutionary pattern. Because of this, many scientist often place these animals under their own sub-kingdom called Parazoa. This means "beside the animals". The phylum porifera is divided into three main groups: the hexactinellida, demospongiae, and the calcarea. Sponges can be found on ocean floors, in shallow water, and even in fresh water. A sponge is mainly a water-filtering system. They do not move and feed of food particles floating around in the water. All poriferans also have a canal system through which water is pumped. Sponges are just cells that surround a water filled space, have no nervous system, and have no tissues or organs. Water enters through pores called ostia and then goes through canals to a spacious chamber called a spongocoel. Finally they leave through large openings called an oscula.
Sponges have no distinct circulatory, respiratory, reproductive, digestive, nervous, or excretory organs and system. They have no definite symmetry, can reproduce sexually and asexually, and often have a skeletal system made of spicules. A typical sponge is made up of three layers. The first is an outer layer made of flattened, contractile epithelial cells. The next lower layer is a non-living gelatinous layer containing amoebocytes. Lastly, there is an inner layer of flagellated collar cells that circulate sea water inside and through the sponge to carry in food and reproductive products and help waste products exit the sponge. The poriferans do not really have a circulatory system and they all carry out this water-filtering function.
Sponges have no distinct circulatory, respiratory, reproductive, digestive, nervous, or excretory organs and system. They have no definite symmetry, can reproduce sexually and asexually, and often have a skeletal system made of spicules. A typical sponge is made up of three layers. The first is an outer layer made of flattened, contractile epithelial cells. The next lower layer is a non-living gelatinous layer containing amoebocytes. Lastly, there is an inner layer of flagellated collar cells that circulate sea water inside and through the sponge to carry in food and reproductive products and help waste products exit the sponge. The poriferans do not really have a circulatory system and they all carry out this water-filtering function.
Hexactinellida (glass sponge)
They are otherwise known as glass sponges. This class has a skeleton composed of silicone dioxide and have only leuconoid body shapes. They are usually found in the deepest of the ocean floors where the currents are very slow and mild which allow these fragile class of sponges to survive. The hexactinellida have another sub-division called the sclerospongiae which include all coralline and tropical reef sponges.
Demospongiae (largest class)
This class makes up about 90% of all sponges. They are also named horn sponges or bath sponges, in some cases. Their skeleton is composed of protein fibers and only include leuconoid body forms. Demospongiae also have unfused silica spicules, or a tough keratin-like protein called spongin, or both. Their "circulatory" system or water- flowing system is the same for all porifera.
Calcarea (calcareous sponges)
also a generalization of the "circulatory" system of sponges.
They are also named calcareous sponges. Their skeleton is composed of calcium carbonate and are considered the most primitive group of sea sponges. They include asonoid, synocoid, and leuconoid body shapes. The circulatory system is similar to those of other sponges: Water enters through pores called ostia and then goes through canals to a spacious chamber called a spongocoel. Finally they leave through large openings called an oscula.
- James Ikeda