Scientists list around 5,000 species of sponges with only 150 living in fresh water. Sponges belong to the phylum porifera. Sponges can best be described as a simple organism consisting of a combination of cells. Asconoid, syconoid and leuconoid are three different body types of sponges, each with its own distinctive characteristics.
A sponge consists of three layers of cells; the middle layer forms the skeletal structure of the sponge. The outer layer serves as the organism's epidermis while the inner layer provides the cells that push water through the sponge. Pores serve as entryways for water that is pulled into the sponge's body. The phylum name porifera is based upon the presence of these pores. The cells of the sponge take food particles from the water as it passes though its body, thus providing the source of nutrition.
This is the simplest body type of sponges. Its body wall is not folded. Water comes in through openings in its pores known as ostia. Water goes out through an opening called the osculum. Asconoid sponges have a shape like a tube with pores. Leucosolenia is an example of a simple asconoid.
Sponges with syconoid body types possess a body wall that is folded into radial canals. These canals make the syconoid different from the asconoid as the water flows through the canals. Synconoid sponges come in larger sizes than asconoids due to the thicker body wall and longer pores. Synconoids contain a more complex method of transporting water throughout the organism. Scypha is an example of a syconoid.
Leuconoid sponges contain the most complex body form, with the "bath sponge" being an example of a leuconoid. They have the folded wall with canals but its canals have branches that lead into chambers. Cells in each chamber push the water into the next canal. Water flows throughout this relatively complex system before exiting the sponge. Leuconoids consist of many more tissues than the other body types.