SPONGE

any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more. One family, the Spongillidae, is found in fresh water. Adult sponges lack a definite nervous system and do not show conspicuous movements of body parts. (Top) Spongia, (centre) Hippospongia communis, and (bottom) Spongia any member of some 5,000 species of primitive multicellular aquatic animals that constitute the phylum Porifera. Sponges are characterized by the presence of a porous skeleton of interlocking spicules (bony, needlelike structures), glasslike rods, or horny fibres; they live in colonies or as solitary animals attached to the sea bottom or to other solid objects. Commercial natural sponges are the skeletons that support the sponge animal. All of the 5,000 species of sponge are marine except for about 20 freshwater species (Spongilla). They occur in all seas, from the intertidal zone to depths of 8,500 m (more than 28,000 feet), and are most common in warm waters. They range in length from a few centimetres to several metres (an inch to several yards). Some rounded forms may be several metres in diameter. The body shape is variable; it may be fingerlike, treelike, or bushy. Some sponges are tubular; others are flat or shapeless masses. Sponges are divided into three classes: Calcispongiae (Calcarea), Hyalospongiae (Hexactinellida), and Demospongiae. Calcispongiae, or calcareous sponges, are marine sponges containing needlelike or branching spicules of lime. The Hyalospongiae, or glass sponges, have a skeleton often composed of six-rayed spicules of silica; the spicules may be united into a continuous network. The skeletons of some such as that of the Venus's flower basket are often beautiful and prized as curios. The Demospongiae, or siliceous sponges, a class that includes about 80 percent of all sponges, have a skeleton composed of spongin, a plasticlike material. Most are shallow-water species; among them are the commercial bath sponges and the freshwater sponges. The body of the living sponge is covered by a thin, slimy, usually dark epidermal layer consisting of flat cells called pinacocytes. Numerous perforations lead through the skin into a central cavity, the spongocoel, which is lined with choanocytesflagellum-bearing cells. These whiplike structures create currents that draw water into the spongocoel through the perforations; the water passes out through one or several large openings, the oscula (singular osculum). Between the outer and inner cell layers is the mesoglea, a jellylike substance containing free-moving cells known as amoebocytes. The choanocytes ingest food particlesbacteria, other microorganisms, and organic debrisand absorb oxygen from the water current. The amoebocytes produce spherical eggs. After fertilization the larvae swim by means of hairs, or cilia, until they find a suitable site for permanent attachment; they then quickly develop into mature animals. Some species also reproduce by budding, an asexual process in which a section of the adult animal separates and becomes established as a distinct individual. Some sponges live in close association with other animals. The back of the crab Dromia, for example, is always covered with a growth of sponge, which serves as camouflage. Certain spider crabs transplant sponges into their own bodies. Large sponges often harbour smaller organisms that burrow into them but do not feed on the sponge tissue. The boring sponge (clionid) lives on dead and living seashells, disintegrating and absorbing the shell substance. Among the few natural enemies of sponges is a fungus that is sometimes a serious pest of commercial sponges. The so-called bath sponge, or commercial sponge, is obtained mainly from the eastern Mediterranean and from the Gulf of Mexico and the Caribbean Sea (off the western coast of Florida and the West Indies and elsewhere) usually at depths of less than 60 m (200 feet). Sponges are harvested by means of hooks or harpoons used by men in boats, or they are cut from the bottom by skindivers. One of the most commonly used species of commercial sponge is Spongia officinalis, sometimes called the glove sponge, which grows in a variety of shapes and reaches a height of 12 to 15 cm (5 to 6 inches). Hippospongia canaliculata, variety gossypina, the sheep's-wool sponge, is valued for its wooly texture; it has an irregular, shaggy surface. Once in considerable demand, commercial sponges have largely been replaced by synthetic sponges. Additional reading Sponges in general are examined in E.A. Minchin, Porifera, in Ray Lankester (ed.), A Treatise on Zoology, vol. 2 (1900), an ample, classical treatment of the Porifera; Libbie Henrietta Hyman, The Invertebrates, vol. 1, Protozoa Through Ctenophora (1940), pp. 284364, a thorough treatment of the Porifera; Maurice Burton, Sponges (1959), a British Museum (Natural History) report on sponges of the Indian Ocean; Patricia R. Bergquist and C.A. Tizard, Sponge Industry, in F.E. Firth (ed.), The Encyclopedia of Marine Resources (1969), pp. 665670; W.G. Fry (ed.), The Biology of the Porifera (1970), a symposium covering the biology and paleontology of sponges; Klaus Rtzler, The Burrowing Sponges of Bermuda (1974); and Patricia R. Bergquist, Sponges (1978), a comprehensive study of sponge biology. G.C.J. Vosmaer, Bibliography of Sponges 15511913, ed. by G.P. Bidder and C.S. Vosmaer-Roll (1928), is a complete bibliography to 1913.More advanced research includes mile Topsent, Spongiaires de l'Atlantique: provenant des croisires du Prince Albert Ier de Monaco (1928), a well-illustrated monumental classic; D.A Webb, The Histology, Cytology, and Embryology of Sponges, Quarterly Journal of Microscopical Science, 78:5170 (1935), well-documented; A Treatise on Invertebrate Paleontology, pt. E, Archaeocyatha and Porifera (1955), a well-documented systematic account of fossil sponges; Claude Lvi, tude des Halisarca de Roscoff: embryologie et systematique des Dmosponges, Archives de zoologie exprimentale et gnrale, 93:1181 (1956), a fundamental work on the embryology of sponges and its connections with systematics; W.D. Hartman, A Reexamination of Bidder's Classification of the Calcarea, Systematic Zoology, 7:97110 (1958), a critical analysis of the modern classification of Calcispongiae; Maurice Burton, A Revision of the Classification of the Calcareous Sponges (1963), a well-illustrated diagnosis and description of the calcareous sponges of the world; Porifera, in Marcel Florkin and Bradley T. Scheer (eds.), Chemical Zoology, vol. 2, Porifera, Coelenterata, and Platyhelminthes (1968), pp. 176, reviews of various aspects of the biochemistry and physiology of sponges; Tracy L. Simpson, The Cell Biology of Sponges (1984), a well-illustrated, thorough study; Jean Vacelet and Nicole Boury-Esnault (eds.), Taxonomy of Porifera: From the N.E. Atlantic and Mediterranean Sea (1987); Klaus Rtzler, Venka V. Macintyre, and Kathleen P. Smith (eds.), New Perspectives in Sponge Biology (1990), a collection of conference papers; and Louis De Vos, Atlas of Sponge Morphology (1991), a scholarly treatment written in both English and French. Michele Sar The Editors of the Encyclopdia Britannica