Sponges
Sponges belong to the phylum Porifera and are considered the simplest multicellular animals, with over 8,000 species identified. Most sponges inhabit ocean environments, though some freshwater varieties exist. They are anchored to the ocean floor by a stem and can vary in color, including black, brown, gray, red, purple, and green. Sponges are particularly abundant and diverse in tropical and warm temperate waters, where they contribute significantly to marine ecosystems.
These creatures exhibit a unique body structure with an outer layer of cells providing color and an inner layer with flagellate cells that facilitate water movement. Water enters through numerous pores, allowing sponges to filter food and oxygen before expelling waste through a central opening. Sponges possess a skeleton made of spicules, which can be composed of calcium carbonate, silica, or flexible spongin, depending on the species.
Reproduction can occur both sexually, through free-swimming larvae, and asexually via budding or gemmules. Additionally, sponges are well-known for their regenerative capabilities, allowing them to recover from damage. In a commercial context, certain sponges, particularly those with spongin skeletons, are harvested for use in various applications, such as surgical tools, cleaning, and personal care products, with significant harvesting taking place in regions like the eastern Mediterranean and Florida.
Sponges
Bath Sponge Facts
Classification:
Kingdom: Animalia
Phylum: Porifera
Class: Demospongiae
Family: Spongidae
Genus and species:Spongia adriatica
Geographical location: Tropical and subtropical Adriatic Sea, the Mediterranean, the Gulf of Mexico, and the Caribbean
Habitat: Oceans and seas
Gestational period: Sexually, eggs are fertilized by sperm from a nearby sponge, and resultant larvae become sponges; asexually, pieces of sponge break off, settle down, and grow (regenerate), or buds or gemmules form new bath sponges
Life span: Indefinite and dependent on the environment
Special anatomy: As sponges are the most basic form of animal life, there is little anatomy at all
Sponges make up the phylum Porifera, the simplest multicellular animals. There are over eight thousand of sponge species. Most inhabit oceans, although freshwater species exist. Each saltwater sponge has a stem that attaches it to a rock or other object on the ocean floor. Sponge remains are found in the oldest fossil-bearing rocks.
Live sponges can be black, brown, gray, red, purple, or green. They are abundant in Earth’s oceans, from shallows to huge depths and from the equator to the Arctic. However, sponges are most numerous and varied in tropical to warm temperate habitats. The four sponge groups are the marine Calcarea, with calcium carbonate skeletons; deep sea Hexactinellida (glass sponges), with silica skeletons; marine and freshwater Demospongiae, comprising 95 percent of species, with skeletons made of flexible spongin (as in a bath sponge) and/or silica; and Sclerospongiae, with silica-, spongin- and calcium-containing skeletons.
The Physical Nature of Sponges
Live sponges have outer layers of cells, which provide their color, and inner-layer flagellate cells that move water. The simplest sponge is a tube with many pores (ostia) on its surface. Water enters the tube, via ostia, in a current due to flagella attached to inner-layer cells. Flagellate cells absorb oxygen and digest tiny sea creatures. Then water is expelled through an opening, the osculum, atop the tube. Ejection, due to pressure from flagellar movement, moves depleted water away from the sponge, preventing its reuse.
Sponges form groups if a sponge develops young that remain connected to it. As more and more young develop, their body cavities become canal networks. Water then enters via ostia and passes through canals to chambers where flagellate cells absorb food and oxygen. Used water leaves by larger and larger tubes, reentering oceans via an osculum.
Between outer and flagellate cells, a sponge has a skeleton made of structures called spicules. When a sponge dies, its flesh decays, and the skeleton remains. There are three sponge skeleton types. Calcarea sponge spicules are made of lime. Hexactinellida (glass) sponges have glassy silica spicules. Some glassy, spicules form attractive skeletons, such as Venus’ flower baskets. In Demospongiae (including freshwater sponges), the skeleton is almost entirely spongin. Spongin skeletons may contain minute spicules of lime, silica, or both. Bath sponge skeletons have no spicules.
Many sponges begin life as fertilized eggs, which divide until becoming free-swimming larvae. Flagella transport larvae until they settle on the ocean bottom and attach to rocks and other objects to become adults. Sponge reproduction can also be asexual via buds or gemmules. Sponges have a great ability to regenerate to replace lost body parts or even most of the body. Some sponges, treated so all their cells are separated but left in water, form a new sponge.
Commercial Sponges
Some Demospongiae have soft, elastic, spongin skeletons that absorb large amounts of water. These qualities have long made them useful tools for surgery, military gun-cleaning, and the cleaning of automobiles, houses, and bodies. The best such sponges come from the eastern Mediterranean, off the Syrian and Greek coasts. Sponges are also fished for off Tampa Bay, Tarpon Springs, the Florida Keys, and the Bahamas.
In deep waters, suited sponge divers descend into the sea to dredge sponges. In shallow waters off Florida, glass-bottomed boats from a mother ship are used. A pole ending in a pronged hook loosens sponges sighted and brings them to the surface. On return to the mother ship, sponges are spread on deck until their flesh decays, hung to dry in the rigging, or kept in seaside pens, which tides fill and empty, removing sponge tissues and leaving skeletons.
Principal Terms
Flagellum: a long cell extension used in locomotion
Gemmule: an asexual reproductive structure that becomes a new sponge
Intersex: an organism having male and female reproductive organs
Osculum: an opening through which a sponge ejects water
Ostium: a surface pore through which water enters a sponge
Spicule: a needlelike structure that is part of a sponge skeleton
Spongin: a fibrous skeletal material in soft sponges
Bibliography
Bergquist, Patricia R. Sponges. Berkeley: University of California Press, 1978.
Esbensen, Barbara Justis. Sponges Are Skeletons. New York: HarperCollins, 1993.
Hartman, Willard D., Jobst W. Wendt, and Felix Weidenmayer. Living and Fossil Sponges: Notes for a Short Course. Miami: University of Miami, 1980.
Jacobson, Morris K. Wonders of Sponges. New York: Dodd, Mead, 1976.
Van Soest, R. W. M., B. Picton, and C. Morrow. Sponges of the North East Atlantic. New York: Springer Verlag, 2000.
“What Is a Sponge?” NOAA's National Ocean Service, oceanservice.noaa.gov/facts/sponge.html. Accessed 4 July 2023.
Wiedenmayer, Felix. Shallow-Water Sponges of the Western Bahamas. Basel, Switzerland: Birkhäuser, 1977. This book classifies and describes sponges found in the waters off the Bahamas.