Sponge, a simple, aquatic animal that looks like a plant. The term is also used for the skeleton of certain types of these animals; the skeleton soaks up fluid easily. Most sponges live in warm water at shallow depths, although sponges are found in all oceans at various depths. There are also species of sponges that live in freshwater. Sponges usually occur in colonies. When young, they attach themselves to rocks, corals, shells, or other submerged objects. Some species live on sand or mud bottoms.

SpongesSponges do not have heads, arms, or internal organs.

Sponges are an important source of certain drugs with antibiotic and cancer-inhibiting properties. Sponge skeletons that soak up fluid easily are used for washing, cleaning, and painting. However, artificial sponges made from cellulose, rubber, or plastics have greatly reduced their commercial importance.

There are more than 5,000 species of sponges; about 150 species live in freshwater. The body consists of a jellylike mass of tissue clinging to a skeleton. The entire animal is permeated by an extensive system of canals. The surface contains numerous small entrance pores, called ostia, and larger exit holes, called oscula. The canals provide shelter for thousands of small aquatic animals that live there, either permanently or temporarily.

The canals are lined with whiplike cells called choanocytes, the movements of which create currents that cause water to flow through the canals. In passing through the sponge, the water gives up oxygen and food and carries away waste products. The food, absorbed by choanocytes and amoeba-like cells called amebocytes, consists of bacteria and particles of decomposed animals and plants.

Sponges have cells called pinacocytes that function as simple muscles. Pinacocytes cover the exterior surface of a sponge and contract to decrease the size of the sponge and the rate of water flow.

Sponges occur in many colors, including gray, red, yellow, and blue; some appear green because of algae that grow on their bodies. Sponges range in length from one-quarter inch (5 mm) to six feet (1.8 m). They have the remarkable ability to restore lost parts, and a new sponge can grow from a small cutting removed from another sponge.

Sponges use both sexual and asexual methods of reproduction. In the sexual method, larvae develop from fertilized egg cells. A larva swims about until it attaches itself to an object; it then develops into a new sponge. In the asexual method, small buds, or gemmules, break off from the parent and develop into new sponges.

A sponge's skeleton is made up of protein fibers called spongin; of spicules, which are microscopic needles composed of calcium carbonate or silica; or of a combination of fibers and spicules. Spongin sponges are soft; silica sponges are hard and fragile, resembling glass. Most sponges, including those shown in the photographs above, are of the combination type.

Sponge Fishing

Many sponges come from the eastern Mediterranean Sea, the West Indies, and the Tarpon Springs area of Florida. Hookers, workers in sponge-fishing boats, collect the animals from shallow water using long poles equipped with two- or three-pronged hooks. Softer sponges come from depths of 100 feet (30 m) or more and are cut from rocks by divers. In some parts of the Mediterranean sponges are taken by dredging.

When first brought to the surface, the sponges resemble pieces of raw liver. They are beaten and scraped to rid the skeletons of the dead tissue, and then they are washed and dried. Before reaching retail stores they are sorted, washed again, bleached, trimmed, and sometimes dyed.

Sponges form the phylum Porifera (porebearers). The vase sponge is Ircinia campana; the tube sponge, Callyspongia vaginalis; the red beard sponge, Microciona prolifera; the breadcrumb sponge, Halichondria panicea.