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Sea sponges are not plants as many people believe. They are the most primitive animals on the planet. Sponges are multi-cellular but they do not have any organs, muscles or nerves. Experts have identified over 5,000 unique sponge species, including 150 freshwater species. They do not move, and often provide homes for plants and other species. The scientific term for a sponge is “porifera.” While all porifera have commonalities, they are also organized into three distinct classes.
A sponge has a skeleton-like network of “spicules” that maintain its structure. Sponges are organized into classes based on what type of spicules are present. All sponges eat by absorbing microscopic particles in the water by pumping water through canals in the sponge. They vary greatly in size, shape and color. Sea sponges can live from 20 to 100 years. There are three basic body shapes for sponges. Asconoid sponges are perforated tubes. Synconoid sponges are larger than asconoid sponges, with thicker walls. Leuconoid sponges are the most complex of all sea sponges, and also tend to be the largest, with multiple canals.
Calcareous sponges are the most primitive sponges, and the only class of sponges that includes asconoid and synconoid varieties. They consist solely of large, structural spicules made of calcium carbonate. There are around 400 species of calcareous sponges. They live primarily in shallower water in more temperate regions. In tropical regions, calcareous sponges can be found on coral reefs. Most of these sponges are small and dull-colored.
Glass sponges, or Hexactinellida, exist worldwide in deep water. They are most prevalent in the Antarctic. A glass sponge is typically shaped like an upright cylinder rising from the ocean floor. They tend to be pale in color, and their skeleton is composed solely of silica. Although they may look like the tubular synconoid sponges, they are more complex. All glass sponges are leuconoid sponges. Because they exist at such depths, humans have little contact with glass sponges. However, the University of Michigan Museum of Zoology reports they are given as wedding gifts in Japan.
The Demospongiae class of sponges is the largest of the three classes, and includes around 90% of all known species. All members of this class are of the complex leuconoid structure. These are the sea sponges many people envision when they think of sea sponges generally. They can grow quite large and are often brightly colored. Bath sponges are demospongiae sponges. Divers harvest them and they are bleached and sold commercially. They can also be grown in tanks by retailers for sale.
- Sea World: Sponges
- University of Michigan Museum of Zoology: Animal Diversity Web: Porifera Sponges
- University of Michigan Museum of Zoology: Animal Diversity Web: Calcarea Sponges
- University of Michigan Museum of Zoology: Animal Diversity Web: Demospongiae
- University of Michigan Museum of Zoology: Animal Diversity Web: Hexactinellida
- Comstock Images/Comstock/Getty Images