The sponge, in the phylum Porifera, is a very primitive and specialized animal. They are sessile for the majority of their lives, living at depths up to 29,000+ feet underwater. With over 8,000 species of sponge ranging in size from 1mm to 2 meters, it is somewhat surprising only around 150 species of sponge (in the family Spongillidae) have adapted to live in fresh water. Sponges are extremely odd in the sense that their cells do not form tissues (as they do in other animals), they can regenerate body parts, and that they are one of the few asymmetrical animals. Depending heavily upon their environment, a sponge may be a wide range of colors, including red, yellow, orange, brown, and black.
Reproduction Sponges can reproduce both sexually and asexually.
Most sponges are hermaphroditic, having both the male and female reproductive capabilities. The sperm of one sponge can be released into the water, being carried by the current until it reaches another sponge. The sperm then enters another sponge through the collar cell (a cell with flagellum, used mostly for pulling in water containing nutrients). The cell then loses its flagellum and becomes a carrier cell, carrying the sperm to the eggs to be fertilized. The fertilized embryo becomes a solid cell surrounded on the outside by cells with flagellua for movement. It is then released through the oscullum where it will swim for some time (between hours and days) before settling and maturing into an adult sponge.
Asexual reproduction is also quite common among sponges. The most well-known method of asexual reproduction is through gemmulation. Gemmules "are groups of cells that have become enclosed by a tough outer covering1" and released into the water. The gemmules "serve as a normal reproductive process" in some situations. In others, they are "a means to carry the sponges over periods of unfavourable conditions when the adults degenerate,"2 such as an extreme change in temperature. Sponges are also able to reproduce by budding. This takes place when a piece of a sponge is broken off. The broken piece can then regrow into a fully developed sponge.
Digestion Sponges have many small holes throughout their bodies known as pores. Flagella along the outside of the sponge bring water into it, along with any nutrients that may be in the water. As these nutrients enter the sponge, they are engulfed by the collar cells and digested there, or transported to the amoeboid cells for digestion.
Nervous System Sponges have no real nervous system.
Excretion A sponge removes wastes through its pores as water travel into and out of the sponge. The largest pore is the oscullum, the wide opening found on the anterior of the sponge, and outwardly projects water containing wastes from the sponge. Circulation Sponges are aquiferous (they carry water). Other than this, however, there is no circulation in the sponge.