When you look at a sponge, the category "animal" might not necessarily come to mind, but sponges are animals. There are over 5,000 species of sponges (Source: EOL), and most live in the marine environment, although there are freshwater sponges.
Sponges are classified in the phylum Porifera, a word that comes from the Latin words porus (pore) and ferre (bear), meaning "pore-bearer". This is a reference to the numerous holes (pores) on the sponge's surface. It is through these pores that the sponge draws in water from which it feeds.
Sponges come in a wide variety of colors, shapes and sizes. Some, like the liver sponge pictuerd here, look like a low-lying crust on a rock, while others can be taller than humans. Some sponges are in the form of encrustations or masses, some are branched, and some look like tall vases (e.g., see vase sponge image by clicking on the "more images" link above).
Sponges are relatively simple multi-celled animals. Sponges do not have tissues or organs like some animals do, but they have specialized cells to perform necessary functions. These cells each have a job - some are in charge of digestion, some reproduction, some bringing in water so the sponge can filter feed, and some for getting rid of wastes.
The skeleton, or structure of sponges is formed by spicules, which are made of silica (a glass-like material) or calcareous (calcium or calcium carbonate) materials, and spongin, a protein that supports the spicules. Sponge species may be most readily identified by examining their spicules under a microscope.
Sponges do not have a nervous system, so they don't move when touched.
Habitat and Distribution:
Sponges are found on the ocean floor or attached to substrates such as rocks, coral, shells and marine organisms.
Water and wastes are circulated out of the body by pores called oscula (singular: osculum).
Sponges reproduce both sexually and asexually. Sexual reproduction occurs by production of egg and sperm - in some species, this is from the same individual, in others, separate individuals produce eggs and sperm. Fertilization occurs when the gametes are brought into the sponge by currents of water. A larva is formed, and it settles on a substrate where it becomes attached for the rest of its life.
Asexual reproduction occurs by budding (when a part is broken off or one of its branch tips is constricted, and this small piece grows into a new sponge) or by producing packets of cells called gemmules.
Sponges and Humans:
Examples of Sponges:
There are thousands of sponge species, so it's difficult to list them all here, but here are a few:
- Coulombe, D.A. 1984. The Seaside Naturalist. Simon & Schuster: New York.
- Denoble, P. 2011. The Story of Sponge Divers. Alert Diver Online. Accessed January 16, 2012.
- Hendrikse, S. and Merks, A. 2003. Sponge Fishing in Key West and Tarpon Springs. Accessed January 16, 2012.
- Martinez, Andrew J. 2003. Marine Life of the North Atlantic. Aqua Quest Publications, Inc.:New York
- UCMP. Porifera: Life History and Ecology. University of California Museum of Paleontology. Accessed January 16, 2012.