User:Tonei/Notepad/Sponge

Introduction to phylum

The phylum Porifera contains the primitive multicellular aquatic animals commonly referred to as sponges. There are approximately 5,000 distinct species of sponges, which can be found attached to surfaces anywhere from the intertidal zone to as deep as 8,500 metres (29,000 feet) or further. There are three classes within the phylum Porifera; these are the Calcispongiae, Hexactinellida and Demospongiae. About 20% of known sponges fall within Calcispongiae and Hexactinellida; the remainder are classified as Demospongiae And also they grow up 1 to 2cm longBold text.

Digestion and Excretion

Sponges filter feed on food particles captured through their water current system. Water is taken into the sponge through ostia, small pores on the sponge’s body, and flows through the collar cells. The collar cells are specialized cells designed to capture food particles from incoming water. These food particles are made up of microorganisms and organic debris, as well as other organic substances. The water is then moved by the flagella to the osculum, where it is ejected along with any wastes the sponge has produced. Sponges are capable of processing several litres of water a day (analogous to a human drinking 64 glasses of water in a day) and can absorb large quantities of food in the process. However, this is not considered a definite digestive system.

Nervous System

Sponges lack a definite nervous system. Instead, sponges transmit electrical signals through the cell membrane which makes up the sponge's body. This allows the sponge to go through an immediate system shutdown when threatened.

Reproduction

Sponges are able to reproduce sexually or asexually. In sexual reproduction, sperm is released from a sponge and floats through the water, where it is taken into a sponge with eggs and internal fertilization occurs. This produces a motile larval stage of sponge. Asexual reproduction of sponges is through budding, where a small piece of sponge falls off of the main sponge and grows into a new one. When a sponge is in a hostile environment, sponges can also form small structures known as gemmules. These are similar to a bacterium's endospore. Gemmules are made up of amoebocytes surrounded by a layer of spicules and can survive conditions that would kill adult sponges. When the environment becomes less hostile, the gemmule can resume growing.

Respiration and Circulation

Sponges do not have any independent circulatory or respiratory organs. Instead, oxygen and nutrients are directly exchanged with the water flowing through the sponge. Because of this, the speed of the water has a direct effect on the rate of oxygen consumption. This system eliminates the need for circulatory or respiratory organs.

Locomotion

For many years, all sponges were thought to be sessile creatures. However, some sponges are capable of movement. The cells on the edges of the sponge all move in the same direction over a period of time, moving the entire sponge. As the sponge moves, it rearranges its internal structure cell by cell. While this does not provide for fast movement (a sponge’s top speed is only a few millimetres per day), it is sufficient for the sponge’s purposes.

Symmetry

Unlike almost all other animals, sponges are asymmetrical.

Special characteristics.....special adaptations...etc.

The sponge has several self-defense mechanisms not found in other creatures. When a sponge is disturbed, it contracts and seals its pores to prevent toxins from entering its circulation system. Some sponges also excrete toxins which irritate the skin of humans and other animals.

References

"sponge." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 4 May 2005 <http://www.britannica.com/eb/article?tocId=9110257>.

"Sponge." Wikipedia, the free encyclopedia. 2 May 2005, 21:15 UTC. 2 May 2005 <http://en.wikipedia.org/wiki/Sponge>.

Stewart, Doug. "Sponges Get Respect." 1999. International Wildlife Magazine 11 May 2005. <http://www.nwf.org/internationalwildlife/1998/sponges.html>.

Harrison, Frederick W. "Sponge," The World Book Multimedia Encyclopedia, Mac OS X 2002 Edition, World Book, Inc., 2002.